Portable field maintenance tool with resistor network for intrinsically safe operation

ABSTRACT

A portable field maintenance tool may perform one or more tasks, such as communicating with a field device, powering a field device, diagnosing a field device, or diagnosing a communication link in a plant environment to which a field device is connected. The portable field maintenance tool may interact with field devices configured according to a number of different communication protocols, such as the HART protocol and the Fieldbus protocol. The portable field maintenance tool may be energy limited and fault tolerant, and may operate in compliance with Intrinsic Safety standards, enabling use of the portable field maintenance tool in hazardous areas.

RELATED APPLICATIONS

This application claims priority to and the benefit of IndianApplication No. 201621025383, filed Jul. 25, 2016 and titled “PortableField Maintenance Tool with Resistor Network for Intrinsically SafeOperation,” the entire disclosure of which is expressly incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure generally relates to a portable field maintenancetool, and in particular, to a portable field maintenance tool capableuse in a wide variety of environments and situations.

BACKGROUND

Process control systems, like those used in chemical and petroleumprocesses, typically include one or more process controllerscommunicatively coupled to at least one host or operator workstation andto one or more field devices via analog, digital, or combinedanalog/digital communication links.

A process controller (sometimes referred to as a “controller”), which istypically located within the plant environment, receives signals(sometimes referred to as “control inputs”) indicative of processmeasurements and uses the information carried by these signals toimplement control routines that cause the controller to generate controlsignals (sometimes referred to as “control outputs”) based on thecontrol inputs and the internal logic of the control routines. Thecontrollers send the generated control signals over buses or othercommunication links to control operation of field devices. In someinstances, the controllers may coordinate with control routinesimplemented by smart field devices, such as Highway Addressable RemoteTransmitter (HART®), Wireless HART®, and FOUNDATION® Fieldbus (sometimesjust called “Fieldbus”) field devices.

The field devices, which may be, for example, valves, valve positioners,switches, and transmitters (e.g., including temperature, pressure,level, or flow rate sensors), are located within the plant environmentand generally perform physical or process control functions. Forexample, a valve may open or close in response to a control outputreceived from a controller, or may transmit to a controller ameasurement of a process parameter so that the controller can utilizethe measurement as a control input. Smart field devices, such as fielddevices conforming to the Fieldbus protocol, may also perform controlcalculations, alarming functions, and other control functions commonlyimplemented within a process controller. Field devices may be configuredto communicate with controllers and/or other field devices according tovarious communication protocols. For example, a plant may includetraditional analog 4-20 mA field devices, HART® field devices, orFieldbus field devices.

Traditional analog 4-20 mA field devices communicate with a controllervia a two-wire communication link (sometimes called a “loop” or “currentloop”) configured to carry an analog 4-20 mA DC signal indicative of ameasurement or control command. For example, a level transmitter maysense a tank level and transmit via the loop a current signalcorresponding to that measurement (e.g., a 4 mA signal for 0% full, a 12mA signal for 50% full, and a 20 mA signal for 100% full). Thecontroller receives the current signal, determines the tank levelmeasurement based on the current signal, and takes some action based onthe tank level measurement (e.g., opening or closing an inlet valve).Analog 4-20 mA field devices typically come in two varieties: four-wirefield devices and two-wire field devices. A four-wire field devicetypically relies on a first set of wires (i.e., the loop) forcommunication, and a second set of wires for power. A two-wire fielddevice relies on the loop for both communication and power. Thesetwo-wire field devices may be called “loop powered” field devices.

Process plants often implement traditional 4-20 mA systems due to thesimplicity and effectiveness of the design. Unfortunately, traditional4-20 mA current loops only transmit one process signal at a time. Thus,a set-up including a control valve and a flow transmitter on a pipecarrying material may require three separate current loops: one forcarrying a 4-20 mA signal indicative of a control command for the valve(e.g., to move the valve to 60% open); a second for carrying, to thecontroller, a 4-20 mA signal indicative of the valve's actual position(e.g., so the controller knows the degree to which the valve hasresponded to control commands); and a third for carrying, to thecontroller, a 4-20 mA signal indicative of a measured flow (e.g., so thecontroller knows how a change in valve position has affected the flow).As a result, a traditional 4-20 mA set-up in a plant having a largenumber of field devices may require extensive wiring, which can becostly and can lead to complexity when setting up and maintaining thecommunication system.

More recently, the process control industry has moved to implementdigital communications within the process control environment. Forexample, the HART® protocol uses the loop DC magnitude to send andreceive analog signals, but also superimposes an AC digital carriersignal on the DC signal to enable two-way field communication with smartfield instruments. As another example, the Fieldbus protocol providesall-digital communications on a two-wire bus (sometimes called a“trunk,” “segment,” or “Fieldbus segment”). This two-wire Fieldbussegment can be coupled to multiple field devices to provide power to themultiple field devices (via a DC voltage available on the segment) andto enable communication by the field devices (via an AC digitalcommunication signal superimposed on the DC power supply voltage).

These digital communication protocols generally enable more fielddevices to be connected to a particular communication link, support moreand faster communication between the field devices and the controller,and/or allow field devices to send more and different types ofinformation (such as information pertaining to the status andconfiguration of the field device itself) to the process controller.Furthermore, these standard digital protocols enable field devices madeby different manufacturers to be used together within the same processcontrol network.

Regardless of the communication protocol utilized, field devices mayrequire on-site setup, configuration, testing, and maintenance. Forexample, before a field device can be installed at a particular locationat a process control plant, the field device may need to be programmedand may then need to be tested before and after the field device isinstalled. Field devices that are already installed may also need to beregularly checked for maintenance reasons or, for example, when a faultis detected and the field device needs to be diagnosed for service orrepair. Generally speaking, configuration and testing of field devicesare performed on location using a handheld maintenance tool, such as aportable testing device (“PTD”). Because many field devices areinstalled in remote, hard-to-reach locations, it is more convenient fora user to test the installed devices in such remote locations using aPTD rather than using a full configuration and testing device, which canbe heavy, bulky, and non-portable, generally requiring the installedfield device to be transported to the site of the diagnostic device.

When a user, such as a service technician, performs maintenance testingand/or communications with a field device, the PTD is typicallycommunicatively connected to a communication link (e.g., a current loopor Fieldbus segment) or directly to a field device (e.g., viacommunication terminals of the field device). The PTD initially attemptsto communicate with the field device, such as by sending and/orreceiving digital communication signals along the loop or segment. Ifthe current loop or segment is in proper operating condition, thecommunications signals may be sent and/or received without problem.However, if the loop, segment, or field device contains an electricalfault, such as a short or a break, communications may be impeded, and itmay be necessary to diagnose the loop, segment, and/or field device toidentify the fault.

When such a fault is identified, a technician might need to use avariety of other tools to test the field device and/or communicationlink. As an example, the technician may need to carry a multimeter todiagnose the actual signals transmitted or received by the field device.The multimeter is necessary because traditional PTDs are incapable ofaccurately analyzing the electrical characteristics of signals sent orreceived by a field device. As another example, the technician may needto use a portable power supply to power an isolated field device. Thetechnician may need to power an isolated field device, for example, whenthe field device loses power due to a plant-wide power outage or due toan issue with a local power supply. As another example, the technicianmay simply need to take a field device offline for troubleshooting inorder to avoid negatively effecting other field devices and the rest ofthe process control system. The technician may also need to carry amultimeter to measure the current available on a segment or loop, etc.Each of these tools can take up a fair amount of space, and may beinconvenient for a technician to carry in the field. To address thisproblem with carrying multiple tools, manufacturers have developed PTDsthat include a power supply for providing power to a HART loop.Unfortunately, these powered PTDs are typically incapable of providingpower to Fieldbus field devices. Further, typical portable powersupplies and powered PTDs often fail to comply with Intrinsic Safety(IS) standards, and thus cannot be safely used in hazardous areas (e.g.,an environments or atmospheres that are potentially explosive due toexplosive gas or dust).

If a field device is located in a hazardous area, the technician mayneed to verify that each of his or her tools operates in anintrinsically safe manner. When in a hazardous area, a technician'stools may need to comply with IS standards to ensure safe operation.Generally speaking, IS standards require that plant personnel analyzeall equipment attached to a loop or segment (including any PTDs or othertools that will be attached to the loop or segment) to verify that allattached equipment will operate in a safe manner in a hazardousenvironment. More particularly, IS standards impose restrictions onelectrical equipment and wiring in hazardous environments to ensure thatthe electrical equipment and wiring does not ignite an explosion. Tocomply with IS standards, electrical equipment generally needs to bedesigned with two core concepts in mind: energy limitation and faulttolerance.

The first IS concept dictates that an IS device be designed such thatthe total amount of energy available in the device be below a thresholdsufficient to ignite an explosive atmosphere. The energy can beelectrical (e.g., in the form of a spark) or thermal (e.g., in the formof a hot surface). While IS standards can be complex, they generallyrequire that any voltage within a circuit be less than 29 V; that anycurrent within a circuit be under 300 mA; and that the power associatedwith any circuit or circuit component be under 1.3 W. A circuit havingelectrical characteristics exceeding these thresholds may pose anexplosion risk due to arcing or heat.

The second IS concept dictates that that an IS device be designed in afault tolerant manner, such that it maintains safe energy levels evenafter experiencing multiple failures. In short, IS standards reflect aphilosophy that circuit faults are inevitable and that energy levels ofthe circuit must be limited to safe levels when these circuit faultsoccur.

Generally speaking, portable power supplies and powered PTDs are not IScompliant and thus cannot be used in hazardous areas because: (i)portable power supplies and powered PTDs are typically designed suchthat one or more components may exceed energy levels sufficient to riskigniting an explosive atmosphere, and/or (ii) the portable powersupplies and powered PTDs are vulnerable to component failures thatwould result in the portable power supplies or powered PTDs exceedingenergy levels sufficient to risk igniting the explosive atmosphere.

For example, a typical portable power supply may generate a voltageacross its terminals sufficient to risk an explosion in a hazardousenvironment (e.g., above 29 V). Even when designed to supply a voltageof under 29 V, a typical portable power supply does not includefail-safe mechanisms guaranteed to prevent the supplied voltage orcurrent from spiking. Consequently, when in a hazardous environment,technicians needing to provide power to a field device generally mustuninstall the field device and transport the field device to a safe areawhere it can be powered and tested.

SUMMARY

This disclosure describes a portable field maintenance tool configuredfor use in industrial process control systems, environments, and/orplants, which are interchangeably referred to herein as “automation,”“industrial control,” “process control,” or “process” systems,environments, and/or plants. Typically, such systems and plants providecontrol, in a distributed manner, of one or more processes that operateto manufacture, refine, transform, generate, or produce physicalmaterials or products.

The described portable field maintenance tool may power, communicatewith, and/or diagnose field devices and/or communication links connectedto field devices. The portable field maintenance tool may be configuredfor use with field devices configured according to multiplecommunication protocols, such as the Fieldbus protocol and the HARTprotocol. Accordingly, rather than being forced to carry multiple toolsfor servicing different types of field devices, a user need only carrythe portable field maintenance tool. In some instances, the portablefield maintenance tool may be energy limited and fault tolerantsufficient to comply with IS standards. Accordingly, unlike many priorart portable power supplies and PTDs, the portable field maintenancetool can safely be used in hazardous areas.

In an embodiment, the portable field maintenance tool comprises any oneor more of: a housing; a communication interface; a communicationcircuit; and/or a power supply. The communication interface may bedisposed through the housing, and may include an internal portionaccessible within the housing as well as a set of terminals accessibleoutside the housing. The set of terminals may be electricallyconnectable to a field device by way of a wired link configured to carrya composite signal including: (i) a communication signal transmitted toor from the field device, and (ii) a power signal transmitted to thefield device. The communication circuit may: be disposed within thehousing and electrically connected to the internal portion of thecommunication interface; be configured to encode or decode thecommunication signal; and/or include a resistor network having aresistance within a range (e.g., any value between 75 ohms and 750 ohms)to cause a voltage drop, at the set of terminals, associated with thecomposite signal that is: (i) above a minimum voltage thresholdassociated with reading the composite signal, and (ii) below a maximumvoltage threshold. The power supply may: be disposed within the housing;be electrically connected to the internal portion of the communicationinterface and to the communication circuit; and/or be configured totransmit the power signal. The composite signal may include an analog DCsignal that includes the power signal and that varies in amplitude toconvey information, as well as a digital FM communication signalsuperimposed on the analog DC signal. The minimum voltage threshold maybe a minimum peak-to-peak voltage associated with reading thecommunication signal, and may be any value between 50 mV peak-to-peakand 500 mV peak-to-peak (e.g., 120 mV peak-to-peak). The maximum voltagethreshold may be a value selected to remain below a voltage sufficientto generate a spark at the set of terminals. The power supply may beconfigured to transmit the power signal at a voltage that is at or belowthe maximum voltage threshold. The maximum voltage threshold may be anyvalue between 10 V and 30 V. The resistor network may include aplurality of resistors, which may be arranged in a plurality ofsub-networks. The resistor network may include switches (one or more ofwhich may be solid state relays) for switching one or more resistors inor out of the resistor network.

In an embodiment, a method of communicating with a transmitter fielddevice comprises any one or more of: communicatively connecting, via awired link, a set of terminals of a portable field maintenance tool to atransmitter field device; supplying power from the portable fieldmaintenance tool, via the wired link, to the transmitter field device;receiving by the portable field maintenance tool, via the wired link, acommunication signal superimposed on the supplied power; and/or limitinga voltage drop at the set of terminals, associated with thecommunication signal and the supplied power, to between a minimumvoltage threshold and a maximum voltage threshold by: (i) limiting thesupplied power so that the voltage drop does not exceed the maximumvoltage threshold; and (ii) activating or deactivating one or moreresistors of a resistor network disposed within the portable fieldmaintenance tool and electrically connected to the set of terminals sothat the voltage drop remains above the minimum voltage threshold (e.g.,so that the voltage drop exceeds a minimum peak-to-peak voltageassociated with reading the communication signal). The communicationsignal may be an analog DC signal that varies in amplitude to conveyinformation and that is superimposed on the supplied power. Limiting thesupplied power so that the voltage drop does not exceed the maximumvoltage threshold may comprise limiting the supplied power so that thevoltage drop remains below a voltage sufficient to generate a spark atthe set of terminals.

In an embodiment, a method of communicating with an actuator fielddevice comprises any one or more of: communicatively connecting, via awired link, a set of terminals of a portable field maintenance tool toan actuator field device; supplying power from the portable fieldmaintenance tool, via the wired link, to the actuator field device;limiting the supplied power so that the set of terminals do not exceed amaximum electrical threshold; and/or transmitting by the portable fieldmaintenance tool, via the wired link, to the actuator field device acommunication signal superimposed on the supplied power. Limiting thesupplied power so that the set of terminals do not exceed a maximumelectrical threshold may comprise: (i) limiting the supplied power sothat a voltage drop at the set of terminals does not exceed a maximumvoltage threshold (e.g., any value between 21 V and 24 V); (ii) limitingthe supplied power so that power available at the set of terminals doesnot exceed a maximum power threshold (e.g., any value between 0.25 W and1.5 W); (iii) limiting the supplied power so that a current at the setof terminals does not exceed a maximum current threshold (e.g., anyvalue between 25 mA and 31 mA); (iv) inducing a first voltage dropacross an internal resistor to keep a second voltage drop at the set ofterminals below a maximum voltage threshold; and/or (v) disabling theportable field maintenance tool when a voltage at the set of terminalsexceeds a maximum voltage threshold or when a current at the set ofterminals exceeds a maximum current threshold.

In an embodiment, a portable field maintenance tool comprises any one ormore of: a pair of terminals electrically connectable, via a wired link,to a field device that transmits or receives a signal via the wiredlink; a communication circuit, electrically connected to the pair ofterminals, that receives or transmits the signal; an energy measurementcircuit, electrically connected to the pair of terminals, that measuresone or more electrical characteristics of the signal; a resistornetwork; a control unit; and/or a power supply that supplies power viathe wired link. The control unit may: activate or deactivate one or moreresistors of the resistor network based on the measured one or moreelectrical characteristics; and/or control the power supply based on themeasured one or more electrical characteristics (e.g., to prevent thepair of terminals from exceeding a maximum electrical threshold, such asa maximum power threshold). When a current draw at the pair of terminalsincreases, the power supply may prevent the pair of terminals fromexceeding a maximum power threshold by reducing a supplied voltage.

In an embodiment, a method of communicating with a field device andmonitoring signals sent or received by the field device comprises anyone or more of: (i) electrically connecting, via a wired link, a fielddevice to a pair of terminals of a portable field maintenance tool; (ii)transmitting or receiving, at the pair of terminals of the portablefield maintenance tool, a signal to or from the field device; (iii)measuring one or more electrical characteristics of the transmitted orreceived signal; (iv) maintaining a voltage drop at the pair ofterminals to a value above a minimum voltage threshold necessary to readthe signal by activating or deactivating one or more resistors of theportable field maintenance tool based on the measured one or moreelectrical characteristics; (v) disabling the portable field maintenancetool when the signal on the wired link exceeds a maximum electricalthreshold or drops below a minimum electrical threshold; (vi) supplyingpower from the portable field maintenance tool, via the wired link, tothe field device; (vii) adjusting the supplied power to prevent the pairof terminals from exceeding a maximum electrical threshold; and/or(viii) stopping the supplying of power and raising a loop resistance tobleed off voltage associated with the supplying of power by activatingor deactivating one or more resistors of the portable field maintenancetool. In an embodiment, the method includes performing an analysis ofthe one or more electrical characteristics to determine whether or notthe field device is connected to an external loop resistor; preventingan internal loop resistor from activating when the analysis reveals thatthe field device is connected to an external loop resistor; and/oractivating the internal loop resistor when the analysis reveals that thefield device is not connected to an external loop resistor. The methodmay include detecting voltage decay at the pair of terminals andenabling activation of a power supply based on the detected voltagedecay.

BRIEF DESCRIPTION OF THE DRAWINGS

Each of the figures described below depicts one or more aspects of thedisclosed system(s) and/or method(s), according to an embodiment.Wherever possible, the Detailed Description refers to the referencenumerals included in the following figures.

FIG. 1A depicts an example portable field maintenance tool connected toa field device.

FIG. 1B is a block diagram of an example process control system wherethe portable field maintenance tool shown in FIG. 1A may be utilized tocommunicate with, diagnose, or power one or more field devices.

FIG. 2 is a schematic of a prior art passive PTD communicativelyconnected to a HART field device.

FIG. 3 is a schematic of a prior art passive PTD communicativelyconnected to a Fieldbus field device.

FIG. 4 is a block diagram of the portable field maintenance tool shownin FIG. 1A, depicting an example in which the portable field maintenancetool includes an active communicator for powering and communicating withfield devices.

FIG. 5A is a block diagram of an active communicator, configured fordigital frequency modulation communication, that may be found in theportable field maintenance tool shown in FIG. 1A.

FIG. 5B is a block diagram of an active communicator, configured fordigital amplitude modulation communication, that may be found in theportable field maintenance tool shown in FIG. 1A.

FIG. 5C is a block diagram of an active communicator, configured foranalog communication, that may be found in the portable fieldmaintenance tool shown in FIG. 1A.

FIG. 6 is a schematic of an active communicator that may be found in anexample portable field maintenance tool and that may enablecommunication via a digital frequency modulation communication protocol,such as the HART protocol.

FIG. 7 is a schematic of a resistor network shown in FIG. 6.

FIG. 8A is a schematic of the portable field maintenance tool shown inFIG. 6 connected to a transmitter, depicting an example in which thetransmitter is powered by the active communicator of the portable fieldmaintenance tool.

FIG. 8B is a schematic of the portable field maintenance tool shown inFIG. 6 connected to an actuator, depicting an example in which theactuator is powered by the active communicator of the portable fieldmaintenance tool.

FIG. 9A is a schematic of the portable field maintenance tool shown inFIG. 6 connected to a transmitter, depicting an example in which thetransmitter is not powered by the active communicator of the portablefield maintenance tool.

FIG. 9B is a schematic of the portable field maintenance tool shown inFIG. 6 connected to an actuator, depicting an example in which theactuator is not powered by the active communicator of the portable fieldmaintenance tool.

FIG. 10 is a schematic of the portable field maintenance tool shown inFIG. 6 connected to a field device, depicting an example in which apower monitor of the portable field maintenance tool may be connected tothe field device in parallel to measure electrical characteristics ofsignals sent or received by the field device.

FIG. 11 is a schematic of the portable field maintenance tool shown inFIG. 6 connected to a field device, depicting an example in which thepower monitor of the portable field maintenance tool may be connected tothe field device in series to measure electrical characteristics ofsignals sent or received by the field device.

FIG. 12 is a schematic of the portable field maintenance tool shown inFIG. 6 connected to I/O devices, depicting an example in which theportable field maintenance tool may test the I/O devices.

FIG. 13 is a schematic of an active communicator that may be found in anexample portable field maintenance tool and that may enablecommunication via a digital amplitude modulation communication protocol,such as the Fieldbus protocol.

FIG. 14A is a schematic of the portable field maintenance tool shown inFIG. 13, demonstrating an example in which the portable fieldmaintenance tool may be connected to a field device connected to anoperational bus.

FIG. 14B is a schematic of the portable field maintenance tool shown inFIG. 13, demonstrating an example in which the portable fieldmaintenance tool may power and communicate with a field device via aninternal bus of the portable field maintenance tool.

FIG. 15 is a view of a communication interface of the portable fieldmaintenance tool shown in FIG. 1A from a perspective external to theportable field maintenance tool.

DETAILED DESCRIPTION

The present disclosure describes a portable field maintenance tool andvarious techniques for implementing the portable field maintenance tool.FIG. 1A depicts an example portable field maintenance tool 100 (“tool100”) that may be connected to a field device 160 via a communicationlink 150. Advantageously, the tool 100 is capable of not onlycommunicating with the field device 160, but of also powering the fielddevice 160. The tool 100 may utilize a single composite signal,transmitted via the link 150, for both powering and communicating withthe field device 160. In some cases, the tool 100 can diagnose problemswith the field device 160 or with a communication link in the plantenvironment to which the field device 160 is connected (e.g., a HARTloop or Fieldbus segment; not shown). In some instances, the tool 100may communicate with or diagnose field devices configured according todifferent protocols. For example, the tool 100 may be capable ofcommunicating with, powering, and diagnosing traditional 4-20 fielddevices, HART field devices, and Fieldbus field devices. Unlike manyprior art PTDs that force a user to utilize multiple devices and/or toconnect multiple cables and wires to various different terminal sets ifhe or she wants to communicate with a field device, power the fielddevice, and perform diagnostics on signals sent or received by the fielddevice, the tool 100 may utilize a single terminal set forcommunications, power, and diagnostics, simplifying configuration anduse of the tool 100 for users.

Moreover, the tool 100 may be energy limited and fault tolerantsufficient to comply with IS standards. For example, the tool 100 may bedesigned so that all components of the tool 100 and so that all signals(e.g., including power and/or communication signals) transmitted and/orreceived by the tool 100 are energy limited to ranges compliant with ISstandards. Further, the tool 100 may “self-monitor” components of thetool 100 and/or signals transmitted or received by the tool 100 toensure that the components and/or signals remain IS compliant. Toillustrate, the tool 100 may disable one or more components (or disablethe tool 100 entirely) when a component or signal approaches or exceedsa threshold associated with IS standards. Accordingly, when the tool 100is IS compliant, a user can connect the tool 100 to the field device 160or to a link (e.g., a HART loop or Fieldbus segment) to which the fielddevice 160 is connected with confidence that he or she will not violateIS standards and with confidence that he or she will not ignite anexplosive atmosphere. In short, unlike many traditional portable powersupplies and PTDs, the tool 100 may safely be used in hazardous areas.

The communication link 150 may be a two-wire communication link capableof carrying a communication signal and/or a power signal, each of whichmay be part of a composite signal. As used herein, the term “signal” mayrefer to a communication signal, a power signal, or a composite signalconveying both power and information. Generally speaking, the term“communication signal” refers to any signal conveying information (suchas a control signal that commands an actuator to actuate), and may beanalog or digital and AC or DC. The term “power signal” refers to anyelectrical energy transmitted for the purpose of supplying power, andmay be AC or DC. The tool 100 may have a terminal set for connecting tothe link 150 and field device 160, and in some cases may have multipleterminal sets for connecting to field devices configured to variousdifferent protocols (e.g., a terminal set for HART field devices and aterminal set for Fieldbus field devices).

To power the field device 160, the tool 100 may include a power supplyconfigured to supply a voltage across terminals of the tool 100 to whichthe communication link 150 is connected.

The tool 100 may be configured to communicate with the field device 160via a composite signal (transmitted via the link 150) including acommunication signal (to facilitate communication between the tool 100and the field device 160) and a power signal (to provide power to thefield device 160). The communication signal may be a digital signal, ananalog signal, or a composite analog and digital signal. Said anotherway, the tool 100 may transmit and/or receive a first composite signalincluding a power signal and a second composite signal that includes ananalog and digital signal.

For example, the tool 100 may include a first terminal set fortransmitting and/or receiving a first composite signal (e.g., a HARTsignal) including: (i) a DC power signal (e.g., 4 mA), and (ii) a secondcomposite signal for communications (e.g., an AC digital communicationsignal superimposed on a 0-16 mA DC communication signal) superimposedon the 4 mA power signal. In such an example, the power signal generallyremains constant at 4 mA and represents a live zero, resulting in thefirst composite signal having a current magnitude range of 4-20 mA. Thetool 100 may additionally or alternatively have a second terminal setfor transmitting and/or receiving a composite signal according to otherprotocols, such as the Fieldbus protocol. For example, the tool 100 maytransmit and/or receive a composite signal including: (i) a DC powersignal (e.g., 10-25 mA), and (ii) an AC digital communication signal(e.g., modulated at 15-20 mA peak-to-peak) superimposed on the DC powersignal. In some cases, the tool 100 includes one or more terminal setsfor transmitting analog and/or digital communication signals withoutproviding power (e.g., for situations where the field device 160 isalready powered).

As noted, the tool 100 may operate in compliance with IS standards. Thatis, the tool 100 may safely be used in hazardous areas because thecomponents of the tool 100 may be energy limited and fault tolerant inaccordance with IS standards. For example, the components of the tool100 may be (i) current limited to a current limit (e.g., 250 mA, 300 mA,350 mA, etc.) (ii) voltage limited to voltage limit (e.g., 25 V, 29 V,35V, etc.) and (iii) power limited to a power limit (e.g., 1 W, 1.3 W,1.5 W, etc.). The tool 100 may have one or more built-in redundancies(e.g., automatic shutdown, redundant components, etc.) to ensure thatcomponent failure does not result in these energy limitations beingexceeded.

The tool 100 may include any one or more of: a display 122, a housing128, input keys 132, and a folding stand 152. The housing 128 may beshaped and sized as a handheld unit. The housing 128 may have agenerally rectangular cubic shape, or any other desirable shape or size(e.g., 5 inches, 7 inches, or 11 inches measured diagonally).

The display 122 and input keys 132 may be disposed on a front face ofthe housing. The display 122 may be a touchscreen, such as a capacitivetouchscreen that detects touch input via capacitive sensing, or aresistive touchscreen that detects touch input via applied pressure. Theinput keys 32 may be physical keys, such as push buttons ormulti-directional buttons. In some cases, the tool 100 does not includethe input keys 32.

The folding stand 152 may pivot between a flat position against the backof the housing 128 and an outwardly pivoted position from the back ofthe housing 128. In the flat position, a user can carry the tool 100 anduse the tool 100 in a similar manner that one would use a tablet. In theoutwardly pivoted position, the folding stand 152 can be used to propthe maintenance tool 100 in an upright position. In some instances, thetool 100 does not include the folding stand 152.

FIG. 1B is a block diagram of an example process control system 10 wherethe tool 100 may be utilized to communicate with, diagnose, or power oneor more field devices. The process control system 10 includes a processcontroller 11 connected to a data historian 12 and to one or more hostworkstations or computers 13 (which may be any type of personalcomputers, workstations, etc.), each having a display screen 14. Theprocess control system 10 may include a plurality of field devices 160,including field devices 15-22.

The controller 11 may be connected to field devices 15-22 viainput/output (“I/O”) cards 26 and 28. The data historian 12 may be anydesired type of data collection unit having any desired type of memoryand any desired or known software, hardware, or firmware for storingdata. The controller 11 is, in FIG. 1B, communicatively connected to thefield devices 15-22.

Generally, the field devices 15-22 may be any types of devices, such assensors, valves, transmitters, positioners, etc., while the I/O cards 26and 28 may be any types of I/O devices conforming to any desiredcommunication or controller protocol. For example, the field devices15-22 and/or I/O cards 26 and 28 may be configured according to the HARTprotocol or to the Fieldbus protocol. The controller 11 includes aprocessor 23 that implements or oversees one or more process controlroutines 30 (or any module, block, or sub-routine thereof) stored in amemory 24. Generally speaking, the controller 11 communicates with thedevices 15-22, the host computers 13, and the data historian 12 tocontrol a process in any desired manner. Moreover, the controller 11implements a control strategy or scheme using one or more functionblocks 32-38, wherein each function block is an object or other part(e.g., a subroutine) of an overall control routine 30. The functionblocks 32-38 may be stored in and executed by the controller 11 or otherdevices, such as smart field devices.

The tool 100 may be communicatively connected via the link 150 to acommunication link (e.g., a HART loop or Fieldbus Segment) connectingone of the field devices 15-22 to the I/O cards 26 and 28.Alternatively, the tool 100 may be communicatively connected directly toone of the field devices 15-22 (e.g., via communication terminalspresent on the field devices 15-22). If desired, the tool 100 mayprovide power to the field devices 15-22 to which the tool 100 isconnected, or to a bus (e.g., a Fieldbus segment) to which the fielddevices 15-22 are connected. The tool 100 may enable a user tocommunicate with and/or diagnose any one of the field devices 15-22. Insome instances, the tool 100 only powers a single one of the fielddevices 15-22 at any given time.

FIG. 2 is a schematic of a prior art PTD 205 that is connected, via aHART loop 200A, to a HART field device 215 and that requires the use ofa portable power supply 220. Unlike the tool 100, the PTD 205 cannotsupply power to the field device 215, and is thus inconvenient fortechnicians. Further, the portable power supply 220 may not comply withIS standards, making it unsuitable for use in hazardous areas. Finally,unlike the tool 100, the PTD 205 requires a loop resistor 210, connectedin parallel with the PTD 205 to the loop 200A, to communicate with thefield device 215.

As noted, the PTD 205 does not supply power to the field device 215. Thefield device 215 is instead powered by a portable power supply 220. FIG.2 represents a scenario in which the field device 215 is being benchtested or in which the field device 215 is isolated from its normalpower source in the field. Because the PTD 205 does not supply power tothe field device 215, a technician may need to carry the portable powersupply 220, in addition to the PTD 205, to the field device 215 whenservicing it in the field.

As further noted, the power supply 220 may not comply with IS standards.Thus, if the field device 215 is in a hazardous area, the technician maynot be able to supply power to the field device 215, and consequentlymay not be able to utilize the PTD 205 to service the field device 215.Typical portable power supplies often cannot safely be used in hazardousareas because they are usually not compliant with IS standards. Inparticular, typical portable power supplies are often vulnerable tocomponent failures that may result in voltage, current, and/ortemperature spikes sufficient to ignite an explosive atmosphere. Itshould be noted that if the PTD 205 were to be made “active” by adding apower supply, it would suffer many of the same problems suffered byportable power supplies regarding IS standards.

Finally, the PTD 205, like many prior art PTDs, requires the external250 ohm loop resistor 210 to communicate with the HART field device 215.By comparison, the tool 100 may include an internal resistor networkthat provides sufficient resistance to read a signal on a link such asthe loop 200A, and thus does not require the use of the externalresistor 210. The external resistor 210 provides sufficient loopresistance to enable the PTD 205 to detect a voltage on the loop 200A,which is necessary for reading the signal carried by the loop 200A(i.e., the PTD 205 interprets the detected voltage as a signal value).In this example, the PTD 205 might interpret an analog value (e.g., atank level measurement between 0% full and 100% full) based on theparticular value of the detected voltage within a range of 1 V-5 V(e.g., wherein 1 V=0% and 5V=100%). For example, when the loop currentis 20 mA, the PTD 205 detects 5 V (i.e., 20 mA*250) and when the loopcurrent is 4 mA, the PTD detects 1 V (i.e., 4 mA*250). Further, the PTD205 might interpret the digital component of a HART signal based on thedetected voltage. The digital component of a HART signal generallyvaries by about 1 mA peak-to-peak. Thus, the 250 ohm resistor 210enables the PTD 205 to detect a voltage, corresponding to this digitalcomponent, of about 250 mV (1 mA*250). If a smaller resistor were used(or no resistor were used), the voltage associated with the signaling onthe loop 200A might drop to levels undetectable by the passive PTD. Bycomparison, the tool 100 may utilize an internal resistor network havinga resistance below 250 ohms, enabling the tool 100 to read a signal onthe HART loop 200 a while complying with IS energy limitations.

FIG. 3 is a schematic of a prior art PTD 305 communicatively connectedto a Fieldbus field device 310 that is powered by a Fieldbus powersupply 315 via a Fieldbus segment 300. The PTD 305 is similar to the PTD205 in that it does not supply power to the field device 310, and isthus inconvenient for technicians. That is, when a technician isservicing the field device 310, he or she generally relies on the powersupply 315 or a portable power supply (not shown) to power the fielddevice 315. By comparison, the tool 100 can supply power to a fielddevice such as the field device 310, even when the field device 310 islocated in a hazardous area.

FIG. 4 is a block diagram of the tool 100, depicting an example in whichthe tool 100 includes an active communicator 404 and a physicalcommunication interface 406 electrically connected via electricalconnections 416 and 417 to the active communicator 404 so that theactive communicator 404 can power and communicate with the field device160 via the physical communication interface 406, as well as measure oneor more electrical characteristics of signals sent or received by theactive communicator 404. As shown, the communication interface 406 maybe disposed through the housing 128, such that an external portion ofthe interface 406 is accessible outside the housing 128, enabling thecommunication link 150 and field device 160 to be connected to theinterface 406.

The active communicator 404 enables the tool 100 to communicate with thefield device 160, diagnose the field device 160, power the field device160, and/or diagnose a communication link in a plant environment towhich the field device 160 is connected (not shown). In some cases, theactive communicator 404 may be configured to communicate with anddiagnose multiple different types of field devices (e.g., HART fielddevices and Fieldbus field devices), and/or may be configured to complywith IS standards so that it can be used to communicate with, diagnose,and power field devices located in hazardous areas. The one or morepower supplies of the active communicator 404 may include switches fordisabling the power supplies.

The active communicator 404 may include a power supply for supplyingpower to the field device 160, a signal encoder and decoder (e.g., amodem) for communicating with the field device 160, and/or energymeasurement circuitry (e.g., a voltmeter and/or ammeter) for measuringelectrical characteristics of signals sent and received by the activecommunicator 404. The active communicator 404 may transmit or receivecommunication signals to or from the field device 160 via the electricalconnections 416 and 417. The active communicator 404 may encodecommunication signals by modulating a current magnitude or a frequencyto represent an analog or digital value, and may superimpose thecommunication signal on a power signal to create a composite signal.

The tool 100 may include a control unit 402, communicatively coupled tothe active communicator 404 via a communication bus 414, configured tocontrol and monitor the active communicator 404. At a high level, thecontrol unit 402 may activate and deactivate components of the activecommunicator 404 to: (i) configure the active communicator 404 so thatit remains energy limited in accordance with IS standards; (ii)configure the active communicator 404 to communicate according to adesired communication protocol (e.g., HART or Fieldbus); (iii) configurethe active communicator 404 in response to a connection made at thephysical communication interface 406 (e.g., based on whether a userconnects the communication link 150 to a terminal set for HART or aterminal set for Fieldbus); and/or (iv) configure the activecommunicator 404 for a particular field device configuration or fielddevice type (e.g., actuator or transmitter). Generally speaking, atransmitter is a field device configured to obtain a measurement (e.g.,via a temperature sensor, pressure sensor, flow sensor, level sensor,etc.) and to transmit the measurement. The field device configuration ortype may be determined based on user input or based on communicationwith the connected field device.

The control unit 402 may include a processor 422, a memory 424 storingone or more routines, and an I/O interface 426 communicatively coupledto other components of the tool 100 via the bus 414. The routines storedat the memory 424 may include a circuit manager routine 462 foractivating and deactivating components of the active communicator 404 asdescribed above and a diagnostics manager routine 464 for diagnosingsignals sent and received by the active communicator 404.

The tool 100 may also include a user interface (“UI”) 410,communicatively coupled to the control unit 402 via the bus 414, forproviding a user interface and/or for detecting user input received atthe UI 410 (e.g., touch input). The control unit 402 may provide theuser interface at the UI 410 and detect the user input at the UI 410 byexecuting a UI manager 466 stored at the memory 424. The UI 410 mayinclude the display 122 shown in FIG. 1A, where the control unit 402 mayrender visual output; and an audio device 444 for providing audiooutput. For example, the UI 410 may render a graphical user interfacethat enables a user to select a communication protocol for communicatingwith the field device 160, to select a command to transmit to the fielddevice 160, to view information transmitted from the field device 160 tothe tool 100, etc. The audio device 444 may generate audio alarms ornotifications, for example, in response to alarms transmitted by thefield device 160.

Further, the tool 100 may include a power monitor 408 (e.g., anammeter), communicatively coupled to the control unit 402 via the bus414, for measuring a current or voltage associated with thecommunication link 150 connected to the interface 406. The diagnosticsmanager 464 of the control unit 402 may utilize the power monitor 408 tomeasure a signal transmitted and/or received by the tool 100 todetermine whether the signal has electrical characteristics within anexpected range for a particular protocol. For example, if a userutilizes the tool 100 to attempt to command a HART valve to open to 50%,the power monitor 408 may be utilized to verify that the transmittedsignal has a current at or near a level that will enable the HART valveto properly interpret the signal (e.g., 12 mA). The UI manager 464 maydisplay measurements obtained by the power monitor 408. In some cases,the tool 100 does not include the power monitor 408. However, regardlessof whether the tool 100 includes the power monitor 408, the tool 100 mayrely on electrical measurements obtained by the active communicator 404.

The tool 100 may also include a wireless communication interface 412,communicatively coupled to the control unit 402 via the bus 414, fortransmitting and/or receiving wireless signals, enabling the tool 100 tocommunicate with other components of the plant 10. The wirelessinterface 412 may support one or more suitable wireless protocols, suchas Wi-Fi (e.g., an 802.11 protocol), Bluetooth (e.g., 2.4 to 2.485 GHz),near-field communications (e.g., 13.56 MHz), high frequency systems(e.g., 900 MHz, 2.4 GHz, and 5.6 GHz communication systems), etc. Insome cases, the tool 100 does not include the wireless communicationinterface 412.

FIGS. 5A-5C are block diagrams of active communicators 501, 511, and521, each of which is an example of the active communicator 404 shown inFIG. 4, that are configured to communicate according to differentcommunication schemes. Depending on the embodiment, each of the activecommunicators 501, 511, and 512 may be communicatively coupled to thecontrol unit 402 via the bus 414 and may be electrically connected tothe communication interface 406 via the electrical connections 416 and417 shown in FIG. 4.

The active communicator 501 shown in FIG. 5A is a digital frequencymodulation (“FM”) circuit, and may include a power supply 502 and an FMmodem 504, each of which may be electrically connected, directly orindirectly, to the electrical connection 416 and 417. The power supply502 may provide power to the field device 160 connected to the interface406 via a DC signal. The FM modem 504 may transmit information to and/orreceive information from the field device 160 (via the interface 406)using a frequency modulation scheme, such as the HART protocol. Forexample, to transmit information, the FM modem 504 may superimpose an ACcommunication signal onto a DC signal provided by the power supply 502.The FM modem 504 may encode digital communication signals by modulatingthe frequency of an AC communication signal, wherein a first frequency(or frequency range) represents a digital 0 and a second frequency (orfrequency range) represents a digital 1. For example, the FM modem 504may encode a communication signal by modulating the frequency of thecommunication signal at 1200 Hz (representing a digital 1) and 2200 Hz(representing a digital 0). To receive information, the FM modem 504 mayinterpret a first frequency or frequency range as a digital 0, and mayinterpret a second frequency or frequency range as a digital 1.

The active communicator 511 shown in FIG. 5B is a digital amplitudemodulation (“AM”) circuit, and may include a power supply 512 and an AMmodem 514, each of which may be electrically connected, directly orindirectly, to the electrical connections 416 and 417. The power supply512 may provide power to the field device 160 connected to the interface406 via a DC signal. The AM modem 514 may transmit information to and/orreceive information from the field device 160 using an amplitudemodulation scheme, such as the Fieldbus protocol. For example, totransmit information, the AM modem 511 may superimpose an ACcommunication signal onto a DC signal provided by the power supply 512.The AM modem 511 may encode digital communication signals by modulatingthe amplitude of an AC communication signal, wherein a first amplitude(or amplitude range) represents a digital 0 and a second amplitude (oramplitude range) represents a digital 1. For example, the first rangemay be 7.5 mA to 10 mA and the second range may be −7.5 mA to −10 mA. Insome circumstances, transitions from the first amplitude or amplituderange to the second amplitude or amplitude range may represent a digital0, and transitions from the second amplitude to the first amplitude mayrepresent a digital 1. Thus, the AM modem 514 may control the currentmagnitude of the communication signal to cause transitions between thefirst and second range to encode digital 1s and 0s onto thecommunication signal. To receive information, the AM modem 514 mayinterpret a first amplitude, amplitude range, and/or transition betweenamplitudes (e.g., high-to-low) as a digital 0, and may interpret asecond amplitude, amplitude range, and/or transition between amplitudes(e.g., low-to-high) as a digital 1.

Turning to FIG. 5C, the active communicator 521 is an analog circuit,and may include a power supply 522, a DC current controller or currentsink 524, and/or a DC current monitor 526, each of which may beelectrically connected, directly or indirectly, to the electricalconnections 416 and 417. The active communicator 521 may encodeinformation by causing the current controller 524 to draw current at aparticular magnitude within a range (e.g., 4-20 mA). Example informationencoded by the active communicator 521 includes a command to open avalve to 100% open (e.g., 20 mA) or to 0% open (e.g., 4 mA). The fielddevice 160 that receives the encoded signal may be configured to receivethe signal and interpret the current magnitude as a particular commandor value. The active communicator 521 may additionally or alternativelydecode a signal from a field device 160 by measuring, via the currentmonitor 526, the current magnitude of the received signal. Exampleinformation encoded by a field device 160 (to be decoded by the activecommunicator 521 and/or control unit 402) includes a flow measurement(e.g., wherein the field device 160 is calibrated to report measurementswithin a range of 0-100 gallons per minute by transmitting acorresponding 4-20 mA signal).

In some cases, the tool 100 may include only one of the activecommunicators 501, 511, and 521; while in other cases, the tool 100 mayinclude two or more of the active communicators 501, 511, and 521. Whenthe tool 100 includes multiple ones of the active communicators 501,511, and 521, the tool 100 may be capable of communicating with and/ordiagnosing multiple field devices that operate according to differentprotocols (e.g., HART field devices and Fieldbus field devices).Advantageously, a user can carry a single tool in the plant for testingmultiple types of field devices, saving the user the trouble of carryinga different tool for each different type of field device.

When the tool 100 includes multiple ones of the active communicators501, 511, and 521, the interface 406 may include a terminal set for eachof the active communicators 501, 511, and 521. In some instances, theactive communicators 501 and 521 may share a power supply and/or aterminal set. In such instances, the active communicators 501 and 521may utilize a single composite signal that is modulated in both currentamplitude and frequency to carry information. For example, the activecommunicator 521 may transmit and/or receive information by varying ormeasuring an amplitude of a DC signal between 4-20 mA. The activecommunicator 501 may then superimpose an AC communication signal (e.g.,1 mA peak-to-peak) onto the modulated DC signal.

FIG. 6 is a schematic of an active communicator 600 (which may be anexample of the active communicator 404 shown in FIG. 4) for the tool 100that may be electrically connected to the field device 160 shown in FIG.1A via the communication interface 406 to: (i) supply power to the fielddevice 160 by way of a DC signal (e.g., 4 mA); (ii) communicate with thefield device 160 by way of a current modulated signal biased (e.g., at4-20 mA) on top of the DC power signal; and (iii) communicate with thefield device 160 by way of a digital FM signal superimposed on theanalog current modulated signal. Advantageously, the active communicator600 may be utilized to communicate with and/or diagnose HART fielddevices. In some cases, the active communicator 600 may be energylimited and fault tolerant according to IS standards, and enabling theactive communicator 600 and the tool 100 to power, communicate with,and/or diagnose field devices and communication links located inhazardous areas.

As noted, the active communicator 600 may communicate with the fielddevice 160 utilizing two simultaneous communication channels: a currentmodulated analog signal and a frequency modulated digital signalsuperimposed on the analog signal. Generally speaking, the analog signalcommunicates a primary measured value (e.g., a flow, pressure,temperature, etc.) when the field device 160 is a transmitter andcommunicates a command (e.g., to open or close a valve) when the fielddevice 160 is an actuator. The digital signal may contain informationfrom the field device 160 including a device status, diagnostics,additional measured or calculated values, etc.

The active communicator 600 may include one or more of the following,each of which may be communicatively coupled to the control unit 402 viaa communication bus (not shown): a power supply 602, a resistor 604, anda communication circuit 609. The communication circuit 609 may includeenergy measurement circuitry (e.g., the voltage monitors 611 and 616)that measures electrical characteristics of signals sent and/or receivedby the tool 100. The diagnostics manager 662 may analyze the electricalcharacteristics to verify the signals are within an expected range for agiven protocol (e.g., 4-20, HART, Fieldbus, etc.) or for IS standards.The power supply 602 may supply the power signal provided by the activecommunicator 600, and the communication circuit 609 may encode anddecode communication signals transmitted and/or received by the activecommunicator 600.

The power supply 602, which may be designed to supply any desiredvoltage (e.g., any value between 20 V and 29 V), may be communicativelycoupled to the control unit 402. In some cases, the power supply 602 maybe designed to never exceed: (i) a maximum voltage threshold (e.g., anydesirable value between 23 V and 30 V), or (ii) a maximum currentthreshold (e.g., any desirable value between 20 mA an 35 mA). In somecases, the power supply 602 may be designed to be voltage limited and/orcurrent limited even when experiencing one or more faults, and/or may bedesigned to perform a ramped start-up or soft start during which itramps to a desired voltage over a period of time, thus mitigatingagainst the chance of current spikes. In some instances, the currentand/or voltage of the power signal provided by the power supply 602 maybe measured so that the control unit 402 can shut down the power supply602 when a measured voltage or current exceeds a maximum threshold orfails to exceed a minimum threshold. A measured voltage exceeding amaximum threshold may indicate that someone added an external powersource to the field device to which the tool 100 is connected, which maycause the loop to violate IS standards and/or may damage components ofthe tool 100 or of other devices connected to the loop. A measuredvoltage failing to exceed a minimum threshold may indicate that acircuit has shorted or that the capacity of the power supply 602 hasbeen exceeded. A measured current exceeding a maximum threshold mayindicate that a circuit has shorted or that the power supply 602 islimited at its maximum load. A measured current failing to exceed aminimum threshold may indicate that no field device is connected to thetool 100.

The power supply 602 may be electrically connected to the communicationinterface 406 via the resistor 604, which may have any desirableresistance (e.g., 200-300 ohms). The resistor 604 may function to inducea voltage drop sufficient to ensure that a voltage drop at thecommunication interface 406 remains below a threshold. For example, ifthe power supply 602 is supplying a current of 25 mA, the resistor 604may induce a voltage drop of 6.25 V (i.e., 0.025 A*250 ohms). In caseswhere the power supply 602 is a 23 V power supply, for example, this mayresult in a maximum potential output voltage of 16.75 V. As shown, theactive communicator 600 also includes a voltage monitor 605 thatmeasures a voltage drop across the resistor 604 and transmits themeasured voltage drop to the control unit 402. The voltage monitor 605may function as a current monitor for the power supply 602. For example,the control unit 604, which may be communicatively coupled to thevoltage monitor 605, may rely on the measured voltage drop to calculatea current flowing through the resistor 604. In some cases, the activecommunicator 600 may include an ammeter placed between the power supply602 and the resistor 604.

As noted, the active communicator 600 may include the communicationcircuit 609, which may include: (i) a DC current controller 610 (such asthe DC current controller 524 in FIG. 5) to transmit a signal bycontrolling the current magnitude of an analog DC signal; (ii) aresistor 613 and voltage monitor 611 for measuring a voltage drop acrossthe resistor 613, which is utilized by the control unit 402 anddiagnostics manager 662 to calculate a current transmitted by the DCcurrent controller 610; (iii) a resistor network 618 for receiving andinterpreting an analog DC signal, and (iv) an FM modem 612 (such as theFM modem 504 in FIG. 5) to communicate by encoding or decoding a digitalFM signal. One or more components of the communication circuit 609 maybe switched out if desired. Generally speaking, the DC currentcontroller 610 is used to transmit DC signals (e.g., 4-20), the resistornetwork 618 is used to receive and interpret DC signals (e.g., 4-20),and the FM modem 612 is used to transmit and receive digital signals(e.g., the digital component of a HART signal superimposed on a 4-20signal). Accordingly, when connected to an actuator, the circuit manager661 of the control unit 402 may activate the DC current controller 610and may disable the resistor network 618. When connected to atransmitter, the circuit manager 662 may activate the resistor network618 and disable the DC current controller 610. Generally speaking, theFM modem 612 will be enabled when connected to both actuators andtransmitters.

The DC current controller 610 may be configured to draw a DC current(e.g., 4-20 mA) when the active communicator 600 is connected to anactuator, and may be controlled by the control unit 402 (e.g., inresponse to a user's input provided at the UI 410). For example, a usermay initiate a command to open a valve to 75% open. Based on thisdetected input, the control unit 402 may cause the DC current controller610 to draw a current corresponding to a command to open the valve to75% open (e.g., 16 mA). The DC current controller 610 may abruptlyadjust current levels or gradually ramp current levels, depending on auser specified value. When the active communicator 600 is connected to atransmitter, the DC current controller 610 may be switched out of thecommunication circuit 609 (via a switch not shown) to avoid interferingwith the DC current modulation of the transmitter.

The resistor network 618 may have any desired resistance (e.g., anydesired value between 100 ohms and 1000 ohms) and may be adjustable(e.g., by the control unit 402). In some instances, the resistor network618 has a resistance of 167 ohms. The voltage monitor 616 may measure avoltage drop across the resistor network 618, which may be utilized tomeasure current flowing through the resistor network 618. As an example,in a HART implementation, the voltage monitor 616 may measure a voltagebetween 3.34 V (20 mA*167 ohms) and 0.668 V (4 mA*167 ohms). The digitalcomponent of the HART signal, which typically modulates at 1 mApeak-to-peak, may be detected as a peak-to-peak voltage across theresistor network 618 of 0.167 V (1 mA*167 ohms). Importantly, this isabove 0.12 V, a minimum voltage threshold typically needed to read thedigital component of a HART signal. The resistor network 618 isdescribed in more detail with reference to FIG. 7.

The FM modem 612, like the FM modem 504, may transmit information and/orreceive information using a frequency modulation scheme, such as theHART protocol. The capacitor 614 filters DC current.

The communication circuit 609 may further include a capacitor 614 inseries with the FM modem 612 to filter DC current so that the FM modem612 can receive and transmit the AC component of the signal, and avoltage monitor 616, communicatively coupled to the control unit 402,configured to measure a voltage drop across the resistor network 618.The control unit 402, knowing the resistance of the resistor network618, may calculate the current flow through the resistor network 618based on the measured voltage.

As noted, the communication circuit 609 may be electrically connected tothe communication interface 406 to send and receive communicationsignals. Further, the power supply 602 may be electrically connected tothe communication interface 406 to supply a power signal to the fielddevice 160 via the communication interface 406. The communicationinterface 406 may include terminals 631-636 for connecting to one ormore field devices, and/or fuses 641 and 642 to limit current flowingthrough the active communicator 600. Generally speaking, the fielddevice 160 may be a transmitter configured to report a measurement bymodulating a DC current (e.g., 4-20 mA) or an actuator configured toactuate in a particular manner in response to the magnitude of areceived DC current (e.g., 4-20 mA).

The communication interface 406 may be electrically connected to thepower monitor 408 shown in FIG. 4, which may include a resistor 651 anda voltage monitor 652. The resistor 651 may have a resistancesufficiently low to avoid a significant voltage drop. In some cases, theresistor 651 has a resistance between 0 and 10 ohms (e.g., 2.43 ohms),which may be selected to minimize the voltage drop over the resistor651. The voltage monitor 652 may measure the voltage drop across theresistor 651 and transmit the measured voltage to the control unit 402.The control unit 402, knowing the resistance of the resistor 651, maycalculate the current flow through the resistor 651. In some cases, afuse may be placed between the terminal 635 and the power monitor 408.

In operation, the active communicator 600 may be configured to operatein a “tool-power mode” (i.e., where the active communicator 600 providespower to the connected field device 160) and in a “loop-power mode”(i.e., where the connected field device 160 relies on, e.g., a portableexternal power supply instead of the active communicator 600 for power).The communication interface 406 may include a first terminal set (e.g.,terminals 631 and 632) for tool-power mode and a second terminal set(e.g., terminals 633 and 634) for loop-power mode. Further, the activecommunicator 600 may be configured to operate in a “transmitterconnection mode” and an “actuator connection mode.” Thus, thecommunication interface 406 may be configured to facilitate fourdifferent configurations or types of connections: (i) tool-powertransmitter connection, wherein the active communicator 600 suppliespower to a transmitter; (ii) loop-power transmitter connection, whereinthe active communicator 600 connects to a powered transmitter fielddevice (in some scenarios the loop to which the loop-powered transmitteris connected includes a loop resistor, enabling communication; in othersthe loop does not include a loop resistor. When a loop resistor is notpresent, the tool 100 may activate or adjust the resistor network 618 toprovide sufficient loop resistance for communication); (iii) tool-poweractuator connection, wherein the active communicator 600 supplies powerto an actuator; and (iv) loop-power actuator connection, wherein theactive communicator 600 connects to a powered actuator (in somescenarios the loop-powered actuator includes a DC current controller; inothers it does not).

For a tool-power transmitter connection, the active communicator 600 mayactivate a “tool-power” mode and/or a “transmitter connection” mode. Theactive communicator 600 may activate one or both of these modes inresponse to user input (e.g., via the screen 122 and/or via the buttons132 shown in FIG. 1A). In some cases, the active communicator 600 mayactivate “tool-power” mode in response to detecting that the terminals631 and 632 have been connected to the field device 160. In other cases,the active communicator 600 instead activates “tool-power” mode based oninput from a user. If desired, the active communicator 600 may performone or more power or communications checks or verifications beforeactivating “tool-power mode.” In some instances, the active communicator600 may activate the “transmitter connection” mode in response todetecting that a connected field device is a transmitter. In otherinstances, the active communicator 600 instead activates the“transmitter connection” mode based on input from a user. Further, theactive communicator 600 may perform a power verification after power isenabled to verify that the field device 160 is behaving as expected(e.g., behaving as expected for a transmitter or actuator). The activecommunicator 600 may also verify that the field device 160 is connected,that power supply limits are not exceeded, and/or that no circuits haveunexpectedly shorted.

For a tool-power transmitter connection, a user may connect atransmitter to the terminals 631 and 632. When connected to atransmitter, the current controller 610 may be switched out of thenetwork via a switch (not shown) because the active communicator 600 isnot modulating DC current to transmit a command. After the transmitterhas been connected, the power supply 602 may ramp up power. Power may beramped slowly to avoid current spikes. Current may flow from the powersupply 602, through the resistor 604 and terminal 631, to thetransmitter. The transmitter may draw a certain level of baselinecurrent for power (e.g., up to 4 mA). The transmitter may then drawadditional current based on its configuration and based on a measurementit has performed (e.g., a measured flow, pressure, tank level, etc.). Asan example, a current draw by the transmitter of 4 mA may represent alive-zero for the transmitter's configured measurement range (e.g., 0gpm), and a current draw by the transmitter of 20 mA may represent ameasurement at the top of the configured measurement range (e.g., 100gpm). A current draw between 4-20 mA may represent a proportionalmeasurement within the configured measurement range (e.g., 12 mA=50gpm). In some instances, the tool 100 generates a high alarm when acurrent of 22.5 mA or higher is detected and/or generates a low alarmwhen a current of 3.75 mA or lower is detected.

Current may flow from the terminal 631 to the transmitter and backthrough the terminal 632, through a switch 641. The received current mayflow to the circuit 609. As noted, the capacitor 614 filters DC currentand the DC current controller 610 may be switched out when the activecommunicator 600 is connected to a transmitter. Accordingly, the DCcomponent of the received signal flows through the resistor network 618,where the voltage monitor 616 may measure the voltage drop across theresistor network 618 so that the control unit 402 can determine themagnitude of the received DC current. The control unit 402 may determinea variable value (e.g., a flow rate) based on the determined magnitude.

Because the capacitor 614 allows AC current to pass, the AC component ofthe signal may flow to the FM modem 612. The FM modem 612 may thendecode a digital signal carried by the received AC component in a mannersimilar to that described regarding the FM modem 504. Further, the FMmodem 612 may also transmit information to the transmitter by encoding adigital signal (superimposed onto the DC signal) in a manner similar tothat described regarding the FM modem 504.

For a loop-power transmitter connection, a user may connect a poweredtransmitter to the terminals 633 and 634. The active communicator 600may activate one or both of “loop-power mode” and/or “transmitterconnection mode” in response to user input (e.g., via the screen 122and/or via the buttons 132 shown in FIG. 1A). In some cases, the activecommunicator 600 activates “loop-power” mode in response to detectingthat the terminals 633 and 634 have been connected to a field device(e.g., via a link 150). In other cases, the active communicator 600instead activates “loop-power” mode based on input from a user. Theactive communicator 600 may activate “loop-power” mode after verifyingthat no voltage exists at any other terminals of the communicationinterface 406.

The tool 100 may include a fuse 642, electrically connected to theterminal 634, configured to limit current to a particular threshold. Insome cases, the fuse 642 is not included. In some cases, the fuse 642 isplaced between the terminal 634 and ground. In the same manner as thatdescribed with respect to the tool-power transmitter connection, thecircuit 609 may decode a DC component of a received signal (e.g., 4-20mA) and may modulate and demodulate an AC component of the signal (e.g.,a superimposed frequency modulated 1 mA peak-to-peak signal) to transmitinformation to and receive information from the transmitter.

For a tool-power actuator connection, a user may connect an actuator tothe terminals 631 and 632. The active communicator 600 activates one orboth of “tool-power mode” and/or “actuator connection mode” in responseto user input (e.g., via the screen 122 and/or via the buttons 132 shownin FIG. 1A). The power supply 602 may supply power to the actuator in amanner similar to that described regarding a tool-power transmitterconnection.

In this mode of operation, a switch (not shown) may activate the DCcurrent controller 610 if the DC current controller 610 is switched outof the circuit 609. The DC current controller 610 may draw a DC current(e.g., 4-20 mA), which may be supplied by the power supply 602 and mayflow through the terminal 631 to the actuator, and then back through theterminal 632 to the DC current controller 610. The magnitude of thecurrent acts as a command for the actuator. The current resistor network618 and voltage monitor 616 may be switched out of the circuit 609 bythe control unit 402 via a switch (not shown) when the DC currentcontroller 610 is active because the circuit 609 is not interpreting amodulated DC current in this mode.

Because the capacitor 614 allows AC current to pass, the AC component ofthe received signal may flow to the FM modem 612. The FM modem 612 maythen decode a digital signal carried by the received AC component in amanner similar to that described regarding the FM modem 504, and the FMmodem 612 may transmit information to the actuator by encoding a digitalsignal (superimposed on the DC signal) in a manner similar to thatdescribed regarding the FM modem 504.

For a loop-power actuator connection, a user may connect a poweredactuator to the terminals 633 and 634, and the active communicator 600may activate one or both of “loop-power mode” and/or “actuatorconnection mode” in response to user input (e.g., via the screen 122and/or via the buttons 132 shown in FIG. 1A). In the same manner as thatdescribed with respect to a tool-power transmitter connection, thecircuit 609 may modulate a DC component of a signal (e.g., 4-20 mA) totransmit a command to the actuator, and may modulate and demodulate anAC component of the signal (e.g., a superimposed frequency modulated 1mA peak-to-peak signal) to transmit information to and receiveinformation from the actuator.

The control unit 402 may include a circuit manager routine 661 formanaging the active communicator 600, and/or a diagnostics managerroutine 662 for analyzing signals sent and/or received by the activecommunicator 600. The diagnostics manager 662 may analyze the signalsbased on measurements obtained from the voltage monitors 605, 611,and/or 616. In some cases, the active communicator 600 includes one ormore voltage monitors that measure a voltage drop across one or more ofthe terminals 631-634 (e.g., across terminals 631 and 632 or acrossterminals 633 and 634). The diagnostics manager 662 may analyze one ormore of these voltage drops prior to the circuit manager 661 activating(i.e., switching in) one or more resistors of the network 618 in orderto (i) protect against activation of the resistor network 618 inparallel with an external loop resistor, and/or (ii) manage a multi-stepprocess for activating the resistor network 618.

First, the circuit manager 661 may protect a user from enabling theresistor network 618 in parallel with an external loop resistor on anexternally powered loop, which might result in a disturbance in the loopcurrent and/or a loss in communication due to insufficient loopresistance. That is, activating the resistor network 618 while connectedin parallel with an external loop resistor may drop the total loopresistance to a value too low for detecting and interpreting digitalcommunications. To illustrate, in some cases the resistor network 618may have a resistance of 250 ohms. Typical external loop resistors havea resistance of 250 ohms. Thus, if the resistor network 618 is activatedin parallel with an external loop resistor, the total loop resistancedrops to 125 ohms, which may not be sufficient resistance to induce areadable voltage drop associated with digital communications. Forexample, HART digital communications, which typically modulate at 1 mApeak-to-peak, generally require a voltage drop of at least 120 mVp-p.Thus, if the total loop resistance is 125 ohms, there is little marginof error before a HART digital signal becomes unreadable. To prevent thetool 100 from activating the resistor network 618 in parallel with anexternal loop resistor, the control unit 402 may cause the FM modem 612to attempt digital communication upon connection. If the digitalcommunication does not succeed, the control unit 402 may prompt the user(e.g., via the display 122 shown in FIGS. 1 and 4) to activate theresistor network 618. In some cases, the tool 100 may prevent theresistor network 618 from activating in parallel with a loop resistor byprompting the user with one or more questions and/or instructions tocause the user to connect the tool 100 with the field device in series.

Second, the measured voltages may be used to manage a multi-step processfor activating the resistor network 618, which may help the tool 100avoid exceeding voltage and/or current thresholds (which mightotherwise, for example, blow the fuse 642). For example, the diagnosticsmanager 662 may obtain a voltage measurement from the voltage monitor605 or from a voltage monitor across the terminals 631 and 632 (notshown). If the diagnostics manager 662 determines the power supplyvoltage for the power supply 602 or for an external power supply exceedsa voltage threshold (e.g., 24 V), the circuit manager 661 may preventthe resistor network 618 from activating. Activation of the resistornetwork 618 in such a scenario could result in excessive current (e.g.,more than 50 mA) flowing through the resistor network 618, which mayblow the fuse 642. If the measured power supply voltage is under thevoltage threshold, the circuit manager 661 may activate the resistornetwork 618 with a resistance of 500 ohms. The diagnostics manager 662may then measure current flow (e.g., based on measurements from thevoltage monitor 616) and, if the measured current is below a threshold(e.g., 22.5 mA) the circuit manager 661 may adjust the resistor network618 to a resistance of 250 ohms or 167 ohms, as desired. The fact thatthe measured current is below a threshold generally indicates that theconnected field device is controlling the current.

The circuit manager 661 may detect a voltage decay across the terminals631 and 632 (e.g., 0.01 V to 0.1 V drop every 50 to 100 msec). Thecircuit manager may take two to ten measurements over a period over 100msec to 1 second. In response to detecting the voltage decay, thecircuit manager 661 may give a user an option to activate the powersupply 602 immediately rather than waiting until the voltage decays tozero.

The circuit manager 661 may activate and/or switch out one or moreresistors in the network 618 when the power supply 602 is turned off toraise the resistance of the network 618 to bleed off voltage from afield device connected to the active communicator 600. Bleeding offvoltage may reduce the wait time needed before the power supply 602 canbe reactivated.

The circuit manager 661 may rely on a temperature sensor (not shown)disposed near the network 618 to compensate for changes in resistanceattributable to temperature changes, enabling the circuit manager 661 tomore accurately calculate a current flow based on measurements from thevoltage monitor 616.

The circuit manager 661 may cause the DC current controller 610 togradually change current. For example, the circuit manager 661 mayimplement a gradual current change in response to user input specifyinga change in current over a certain number of seconds (e.g., 1, 2, 3, 4,. . . , 60 seconds, etc.).

The diagnostics manager 662 may perform one or more of the following: aloop test, a device simulation, a recorder calibration, a valvestroking, a DCS output check, a DCS input check, a zero trimcalibration, or a check for isolating cable damage.

For the loop test, a user may connect a field device to: (i) theterminal set 631 and 632 or the terminal set 633 and 634, and (ii) thepower monitor 408. The diagnostics manager 662 may cause the FM modem612 to transmit a communication signal to the field device commandingthe field device to draw current at various levels (e.g., 4 mA, 12 mA,20 mA). The power monitor 408 measures the current transmitted by thefield device in response. The diagnostics manager 662 may cause the tool100 to display the requested current level and the transmitted currentlevel, enabling the user to determine if the transmitter isappropriately responding to the commands.

For device simulation, a user may wire the tool 100 (e.g., via theterminals 631 and 632 of the active communicator 600) to a communicationlink in place of a field device. The diagnostics manager 662 may causethe DC current controller 610 to transmit DC current at a number oflevels (e.g., in response to user input). The user, or a second user,may then verify that the connected process controller received theappropriate values.

For recorder calibration, a user may wire the tool 100 to an analogrecorder and may cause the tool 100 to transmit via the DC currentcontroller 610 preselected current values to the recorder. The user maythen verify that the audio recorder received the preselected values.

For valve stroking, a user may wire the tool 100 to a valve. Thediagnostics manager 662 may transmit a 4 mA signal to the valve, and theuser may set a full closed stop on the valve (e.g., thereby calibratingthe valve so that the full closed position corresponds to a 4 mAsignal). The diagnostics manager 662 may transmit a 20 mA signal to thevalve (e.g., in response to user input), and the user may set a fullopen stop on the valve (e.g., thereby calibrating the valve so that thefull open position corresponds to a 20 mA signal). The diagnosticsmanager 662 may then perform a step test (e.g., in response to userinput) with the DC current controller 610, transmitting current at anumber of levels between 4 mA and 20 mA, to verify that the valve isappropriately calibrated to a 4-20 mA signal.

To check a DCS output, a user may wire the tool 100 to an I/O card thatis typically connected to a field device (e.g., an actuator) and that isconfigured to transmit to the field device a 4-20 mA signal forcontrolling the field device. A user may coordinate (e.g., via radio)with a second user to cause a number of commands to be sent to thedisconnected field device (e.g., to open or close a valve). Thediagnostics manager 662 may read the received signal, and may display acurrent measurement, enabling the user to verify that I/O card istransmitting appropriate signals when attempting to control the fielddevice. The tool 100 may utilize either the power monitor 408 (andterminals 635 and 636) or the voltage monitor 616 (and terminals 631 and632) for the DCS output check.

To check DCS input, a user may wire the tool 100 to an I/O card that istypically connected to a field device (e.g., a transmitter) and that isconfigured to receive from the field device a 4-20 mA signalrepresenting a measurement. The user may cause the tool 100 to send(e.g., via the DC current controller 610) a signal, and may coordinatewith a second user to confirm that the controller connected to the I/Ocard is receiving the proper values.

To perform a zero trim calibration, the tool 100 may implement aprocedure similar to that implemented for the DCS input check. Forexample, a user may connect the tool 100 to a field device, and maycause the field device to run a “device method” that causes the fielddevice to output current at a number of levels. The tool 100 measuresand displays the current from the field device. The user then enters atthe field device the displayed current so that the field device cancalibrate itself based on what it attempted to transmit and what wasactually transmitted. The tool 100 may activate the power supply 602 topower the field device and the resistor network 618 to measure currentfrom the field device, and may measure the current across the resistornetwork 618.

To isolate a damaged cable, a user may utilize the tool 100 to performvoltage measurements at various locations for a cable, at field deviceterminals, at power supply terminals, etc. A large voltage dropindicates damage.

FIG. 7 is a schematic of the resistor network 618 shown in FIG. 6, whichincludes multiple resistors and is configured to withstand failure ofone or more resistors within the network 618 without significantlyaffecting the overall resistance of the network 618. By utilizingmultiple resistors, the resistor network 618 may avoid dramaticincreases or decreases in resistance due to resistor failure, thusavoiding dramatic increases or decreases in voltage drops in thecircuit. For example, if the resistor network 618 were a single resistorthat failed and shorted, the result may be an increased voltage dropacross terminals 631 and 632. Such an increase in the voltage drop atthe terminals 631 and 632 may exceed IS standards and may risk ignitingan explosive atmosphere. Further, by utilizing multiple resistors, eachindividual resistor receives only a portion of the current that entersthe network 618, which may prevent the resistors from overheating andexceeding IS standards.

The resistor network 618 may include a resistor network 702 and aresistor network 704 arranged in parallel, each of which may be switchedout of the resistor network 618 via a switch 706 and a switch 708,respectively. In some instances, the entire resistor network 618 may beswitched out of the circuit 609 (e.g., during power up or when the tool600 is communicating with an actuator). The resistor network 618 mayhave any desirable resistance, e.g., within a range of 100 and 300 ohms(e.g., 167 ohms).

The resistor network 702 may include resistors 712-714, arranged inparallel, and may have a total resistance between 200 and 300 ohms(e.g., 250 ohms). For example, each of the resistors 712-714 may have aresistance of 750 ohms, giving the network 702 a total resistance of 250ohms. Note, the resistor network 702 may have any other combination of aplurality of resistors (including combinations and/or subcombinations ofresistors arranged in series and/or in parallel) resulting in a totalresistance of the network 702 between 200 and 300 ohms. If desired, theresistor network 702 may include a single resistor having a resistancebetween 200 and 300 ohms.

The resistor network 704 may include a resistor network 721 and aresistor network 723, arranged in series, and may have a totalresistance between 400 and 600 ohms (e.g., 500 ohms). The resistornetwork 721 may include resistors 722 and 724, arranged in parallel, andthe resistor network 723 may include resistors 726 and 728, arranged inparallel. Each of the resistors 722-728 may have a resistance of 500ohms, which may give each of the resistor networks 721 and 723 aresistance of 250 ohms (i.e., 1/X=1/500+1/500). Because the resistornetworks 721 and 723 may be arranged in series, the resistor network 704may have a total resistance of 500 ohms. Note, the resistor network 704may have any other combination of a plurality of resistors that resultsin a total resistance between 400 and 600 ohms. For example, theresistor network 704 may include two 1000 ohm resistors arranged inparallel, or may include a single resistor having a resistance of 500ohms.

Regarding the switches 706 and 708, the control unit 402 may: (i)actuate the switch 706 to switch out the resistor network 702 toincrease the resistance of the network 618 (i.e., to the resistance ofthe network 704), or (ii) actuate the switch 708 to switch out theresistor network 704 to increase the resistance of the network 618(i.e., to the resistance of the network 702). The control unit 402 mayincrease the resistance of the network 618 to verify that a field deviceattached to the terminals 633 and 634 is current-controlled below therating of the fuse 642, or to bleed off voltage from the activecommunicator 600 when the power supply 602 is disabled.

In operation, the control unit may switch out one of the networks 702 or704 depending on which of the terminals 631-634 are connected to a fielddevice and/or based on whether the active communicator 600 is providingpower to the field device. For example, in some situations, the activecommunicator 600 may switch out either the network 702 or 704 toincrease the resistance of the network 618 when the active communicator600 is connected to an externally powered field device.

When one or both of the resistor networks 702 and 704 are switched outof the network 618, the control unit 402 may actuate one or both of theswitches 706 and 708 to “activate” both the networks 702 and 704, givingthe resistor network 618 a lower resistance than that of either thenetwork 702 or the network 704. The lower resistance may be desirablewhen operating the active communicator 600 in “tool-power mode” in ahazardous area. IS standards require that the output voltage at theterminals 631 and 632 be lower than what might otherwise be used innormal operation. However, if the voltage at the terminals 631 and 632is dropped too low, the communication signal transmitted or received viathe terminals 631 and 632 may be unreadable. Accordingly, it may beadvantageous to lower the resistance of the network 618 from a valuethat might be used with a traditional communicator (e.g., 250 ohms) to avalue that will result in a lower (but still readable) voltage drop overthe resistor network 618 (e.g., 167 ohms). In some instances, theresistor network 618 may include additional resistor networks (e.g.,1000 ohms) and/or switches, which may be enable the tool 100 to activatethe resistor network when a power supply voltage exceeds 24 V.

One or both of the switches 706 and 708 may be solid state relays, whichmay offer a number of advantages over typical mechanical relays. Forexample, solid state relays can be switched by a lower voltage and lowercurrent than most mechanical relays, making it easier to keep theelectrical signals generated by the tool 100 at levels compliant with ISstandards. Further, unlike typical mechanical relays, solid state relaysgenerally do not generate a spark when operated. Thus, by utilizingsolid state relays with the resistor network 618, the tool 100 can avoidviolating IS standards that might otherwise be violated with mechanicalrelays.

One or more resistors in the resistor network 618 may have a largesurface area designed to facilitate efficient heat dissipation. Forexample, one or more resistors in the resistor network 618 may be size2512 resistors (e.g., 6.3 mm×3.1 mm×0.6 mm). In some cases, one or moreresistors in the network 618 may be size 2010 resistors, size 2020resistors, and/or size 2045 resistors. In some cases, one or moreresistors (or sub-networks) within the resistor network 618 may be ratedfor 2.5 W.

The tool 100 may include a temperature sensor (not shown) to be used inconjunction with the active communicator 600. For example, thetemperature sensor may measure a temperature at or near the resistornetwork 618, which may be utilized by the control unit 402 whencalculating a current through the network 618. This temperaturemeasurement is beneficial because current calculations obtained based onmeasurements from the voltage monitor 616 may be inaccurate when atemperature change increases or decreases the resistance of the network618 to a value different than that assumed by the control unit 402. Inshort, the temperature sensor enables the control unit 402 to compensatefor changes in resistance of the network 618 attributable to temperaturechanges.

FIGS. 8A-12 are schematics of the tool 100, when it includes the activecommunicator 600 shown in FIG. 6, connected to various field devices andI/O devices. FIGS. 8A-12 may not show one or more components of theactive communicator 600 or tool 100. For example, components that are“switched out” or not active may not be shown. Some components may beactive, but may not be shown.

FIG. 8A illustrates an example in which the active communicator 600 isconnected to a transmitter 805 and in which the active communicator 600provides power to the transmitter 805 (i.e., a tool-power transmitterconnection). In such a configuration, a user may connect the activecommunicator 600 to the transmitter 805 via the terminals 631 and 632.The active communicator 600 may power the transmitter 805 by way of thepower supply 602, e.g., transmitting a DC signal of up to 4 mA to thetransmitter 805. Further, the active communicator 600 may engage inone-way analog communication and/or two-way digital communication withthe transmitter 805. To engage in one-way analog communication, theactive communicator 600 may activate a “transmitter connection” mode inwhich the active communicator 600 expects the transmitter 805 tocommunicate by modulating the current magnitude (e.g., between 4-20 mA)of the DC signal provided by the power supply 602. The control unit 402(not shown) may switch the DC current controller 610 (not shown) out ofthe circuit 609 because the transmitter 805, not the circuit 609, maymodulate the DC current flowing between the transmitter 805 and tool100. Note, the FM modem 612 may remain connected to the circuit 609, andmay facilitate two-way digital communication by: (i) transmittinginformation to the transmitter 805 by modulating the frequency of an ACsignal superimposed on the DC signal, and/or (ii) receiving informationfrom the transmitter 805 by demodulating a frequency modulated AC signalsuperimposed on the DC signal by the transmitter 805. The diagnosticsmanager 602 may analyze a signal received from the transmitter 805 basedon measurements obtained from the voltage monitor 616.

FIG. 8B illustrates an example in which the active communicator 600 isconnected to an actuator 855 and in which the active communicator 600provides power to the actuator 855. In such a configuration, a user mayconnect the active communicator 600 to the actuator 855 via theterminals 631 and 632. The active communicator 600 may power theactuator 855 by way of the power supply 602, e.g., transmitting a DCsignal of up to 4 mA to the actuator 855. The active communicator 600may engage in one-way analog communication and/or two-way digitalcommunication with the actuator 855. To engage in one-way analogcommunication, the active communicator 600 may activate an “actuatorconnection” mode in which the active communicator 600 expects theactuator 855 to receive information by interpreting changes in thecurrent magnitude of the DC signal provided by the active communicator600 (e.g., between 4-20 mA). Because the active communicator 600 mayexpect the actuator 855 to receive rather than transmit a currentmodulated DC signal, the control unit 402 may switch the resistornetwork 618 (not shown) and voltage monitor 616 (not shown) out of thecircuit 609 because the network 618 and monitor 616 may not be needed toreceive and interpret a current modulated DC signal. Note, the FM modem612 may remain connected to the circuit 609, and may facilitate two-waydigital communication by: (i) transmitting information to the actuator855 by modulating the frequency of an AC signal superimposed on the DCsignal, and/or (ii) receiving information from the actuator 855 bydemodulating a frequency modulated AC signal superimposed on the DCsignal by the actuator 855.

FIG. 9A illustrates an example in which the circuit 609 of the activecommunicator 600 may be connected to a transmitter 905 and in which thetransmitter 905 is not powered by the active communicator 600. Thetransmitter 905 may be powered by a power supply 910, which may be aportable power supply or a rack-mounted power supply. In some instances,the transmitter 905 may rely on both loop power and the power supply 910for power. A user may connect the circuit 609 to the transmitter 905 viathe terminals 633 and 634. Because the terminals 631 and 632 are notconnected, a closed circuit including the power supply 602 is notformed. The circuit 609 may engage in one-way analog communicationand/or two-way digital communication with the transmitter 905 in amanner similar to that discussed regarding FIG. 8A. The configurationshown in FIG. 9A may be useful when a user encounters a conventionalloop that lacks a loop resistor. In some instances, the tool 100 may beconnected to a loop that already has a loop resistor (e.g., connected tothe negative terminal of the power supply 910). In such cases, the powersupply 910 may be wired to the terminals of the transmitter 905 as onewould expect in normal operation, and the user may connect the terminals633 and 634 to the terminals of the transmitter 905. Alternatively, theuser may connect the terminals 633 and 634 across the already-existingexternal loop resistor.

FIG. 9B illustrates an example in which the circuit 609 of the activecommunicator 600 is connected to an actuator 955 and in which theactuator 955 is not powered by the active communicator 600. The actuator955 may be powered by a power supply 960, which may be a portable powersupply or a rack-mounted power supply. A user may connect the circuit609 to the transmitter 905 via the terminals 633 and 634. Because theterminals 631 and 632 are not connected, a closed circuit including thepower supply 602 is not formed. The circuit 609 may engage in one-wayanalog communication and/or two-way digital communication with theactuator 955 in a manner similar to that discussed regarding FIG. 8B. Insome instances, the power supply 960 may include a DC current controllerthat transmits a DC signal (e.g., 4-20 mA). In such instances, theterminals of the power supply 960 may be connected to the terminals ofthe actuator 955 to form a loop. Further, in such instances a user mayconnect the tool 100 to the terminals of the actuator 955, effectivelyplacing the tool 100 in parallel with the power supply 960.Advantageously, such a connection enables a user to utilize the tool 100without breaking an already existing loop between the actuator 955 andpower supply 960.

FIG. 10 illustrates an example in which the circuit 609 of the tool 100may be connected to a field device 1010 powered by a power supply 1020,and in which the power monitor 408 of the tool 100 may be connected tothe field device 1010 in parallel with the power supply 1020 so that itcan measure electrical characteristics of signals sent or received bythe field device 1010 without disconnecting the field device 1010 fromthe power supply 1020. The field device 1010 may be an actuator or atransmitter; may be powered by a power supply 1020; and may include apositive terminal 1012, a negative terminal 1014, and a test terminal1015. The test terminal 1015 may enable detection of current through thefield device 1010 and/or detection of voltage across the terminals 1012and 1014.

The circuit 609 may be connected to the field device 1010 via theterminals 633 and 634, and via the positive and negative terminals 1012and 1014 of the field device 1010. The power monitor 408 can beconnected to the field device 1010 without breaking the loop between thecircuit 609 and the field device 1010, enabling a user to simultaneouslycommunicate with the field device 1010 via the circuit 609 and to verifythat current, voltage, and/or power measurements associated withcommunication signals between the field device 1010 and the circuit 609are within an expected range. Advantageously, there is no need todisconnect the field device 1010 from the power supply 1020 whenutilizing the power monitor 408 to measure the electricalcharacteristics of the signals received or transmitted by the fielddevice 1010. In some cases, the power supply 1020 may include a DCcurrent controller that send a 4-20 mA signal for controlling the fielddevice 1010 (e.g., when the field device 1010 is an actuator). In suchcases, the DC current controller 610 may be switched out of the circuit,and the tool 100 may function primarily as a digital communicator usingthe FM modem 612.

FIG. 11 illustrates an example in which the circuit 609 of the tool 100may be connected to a field device 1105 powered by a power supply 1120,and in which the power monitor 408 of the tool 100 may be connected tothe field device 1105 in series with the power supply 1120 so that itcan measure electrical characteristics of signals sent or received bythe field device 1010. The power monitor 408 may be connected to thefield device 1105 via the terminals 635 and 636. Because the fielddevice 1105 does not include a test terminal like the field device 1010shown in FIG. 10, the power monitor 408 may be connected to the fielddevice 1105 in series. That is, the positive terminal of the powersupply 1120 may be disconnected from the positive terminal of the fielddevice 1105, and a first terminal from the power monitor 408 (e.g.,terminal 635 or 636) may be connected to the positive terminal of thefield device 1105 and a second terminal from the power monitor 408(e.g., the terminal 635 or 636) may be connected to the positiveterminal of the power supply. In some cases, the power monitor 408 maybe connected in series between the negative terminal of the field device1105 and a loop resistor (not shown) connected to the negative terminalof the power supply 1120. Typically, such a loop resistor can be foundwhen the field device 1105 is a transmitter. In such cases, the resistornetwork 618 may be switched out of the circuit 609.

FIG. 12 illustrates an example in which the circuit 609 of the activecommunicator 600 may be used to test I/O devices. In particular, thecircuit 609 may be connected to an AI card 1205 (which may be connectedto a transmitter) to verify that a signal transmitted by the DC currentcontroller 610 (intended to simulate a transmitter's signal) is properlyreceived by the AI card 1205. Further, the power monitor 408 may beconnected to an AO card 1210 (which may be connected to a controller) toverify communications sent by the controller via the AO card 1210.

FIG. 13 is a schematic of an active communicator 1300 (which may be anexample of the active communicator 404 shown in FIG. 4) for the tool 100that may be electrically connected to the field device 160 shown in FIG.1A via the communication interface 406 to: (i) supply power to the fielddevice 160 by way of a DC signal (e.g., 10-25 mA); and (ii) communicatewith the field device 160 by way of a digital AC signal superimposed onthe DC signal. Advantageously, the active communicator 1300 may beutilized to communicate with and/or diagnose Fieldbus field devices.Further, unlike typical PTDs configured for AM communication, the activecommunicator 1300 can measure current, as well as DC and AC voltages atthe same terminal set that is used for communicating with the fielddevice 160. In some cases, the active communicator 1300 may be energylimited and fault tolerant according to IS standards, and enabling theactive communicator 1300 and the tool 100 to power, communicate with,and/or diagnose field devices and communication links located inhazardous areas.

The active communicator 1300 may be communicatively coupled to thecontrol unit 402, and may include: (i) a bus 1302 electrically connectedto the communication interface 406, (ii) a power supply 1304 configuredto transmit a power signal via the bus 1302, and (iii) a communicationcircuit 1309 configured to communicate with the field device 160 via thebus 1302. The communication circuit 1309 may be configured to send andreceive digital communication signals, which may be amplitude modulatedAC signals (e.g., 15-20 mA peak-to-peak).

The bus 1302 may be referred to as an “internal bus” or “mini-bus,” andmay be disposed at least partially within the housing 128 shown in FIG.1A. The bus 1302 may enable the tool 100 to connect to, communicatewith, and/or power a field device, even when the field device does nothave an active and healthy connection to a bus (such as the fieldbussegment 300 shown in FIG. 3) in the plant environment. By contrast,traditional PTDs that can communicate with a bus-based field devicetypically require that the field device be connected to a functioningexternal bus located in the process plant. The bus 1302 may includeterminators 1321 and 1322 that provide sufficient resistance to enablecommunication on the bus 1302. Each of the terminators 1321 and 1322 mayinclude a resistor (e.g., having a resistance between 90 ohms and 105ohms) in series with a capacitor (e.g., having a capacitance of 1 μF).The bus 1302 may include switches 1322 and 1324 for switching theterminators 1321 and 1322 out of the bus 1302, or for switching the bus1302 completely out of the active communicator 1300 (e.g., when theactive communicator 1300 is connected to a field device alreadyconnected to a healthy bus). Advantageously, the bus 1302 enables afield device to be tested in isolation, allowing a user to more easilyidentify the source of communication problems. For example, a user mayutilize the active communicator 1300 to measure signals transmitted byan externally powered field device, to remove the field device from theexternal power source (e.g., from the powered segment), and to take thesame measurements on the bus 1302, which can be compared to thepreviously obtained measurements.

The circuit 1309 may communicate with the field device 160, which may bea Fieldbus device, via the bus 1302, and may include an AM modem 1310connected in series to a capacitor 1314, the combination of which areelectrically connected in parallel to a DC current controller or sink1312. The AM modem 1310 may transmit to and/or receive information fromthe field device 160 using a digital amplitude modulation scheme (suchas the Fieldbus protocol), and may be the same as or similar to the AMmodem 514 shown in FIG. 5. As an example, the AM modem 1310 may modulateand/or demodulate a signal at 15-20 mA (e.g., −10 mA to 10 mA). Thecapacitor 1314 may filter DC current, allowing only the digitalcommunication signal to pass to the AM modem 514. The DC currentcontroller 1312 may be configured to draw a DC current sufficient toenable the AM modem 1310 to superimpose the communication signal on theDC current without the current dropping below 0 mA. For example, the DCcurrent controller 1312 may draw a DC current of 11 mA, enabling the AMmodem 1310 to superimpose a 20 mA signal on the DC current so that thetotal current on the wires connected to the communication interface 406varies from 1 mA to 21 mA.

The communication interface 406 may include terminals 1331-1333. Thefield device 160 may be connected to the terminals 1332 and 1333 toestablish a communication link between the field device 160 and thecircuit 1309. If a user wishes to supply power to the field device 160using the tool 100, the user may place a shunt between the terminal 1331and the terminal 1332. Placing the shunt between the terminals 1331 and1332 may activate the bus 1302, which may create sufficient loadimpedance to ensure communication signals transmitted via the terminals1332 and 1333 are within an expected range such that the AM modem 1310and/or the field device 160 can interpret the communication signals(e.g., between 0.5 and 1.5 Vpp). The communication interface 406 mayinclude a fuse 1342, electrically connected in series with the terminal1333, that has a resistance of 11 ohms and that is rated for 50 mA. Insome cases, the active communicator 1300 does not include the fuse 1342.In some cases, the fuse 1342 may be placed between the terminal 1333 andground.

The power supply 1304 may be configured to supply a power signal on thebus 1302 at a voltage between 15 V and 20 V (e.g., 17 V). The powersupply 1304 may be a transformer-based power supply, and may “shift” itsground with respect to the terminal 1333. The power supply 1304 may beconfigured to limit a voltage drop across the terminals 1332 and 1333 toa threshold consistent with IS standards. For example, in some cases themaximum allowable output voltage is limited to 15 V at no load. Theoutput voltage at full load may be 10.5 V. The power supply 1304 may becurrent limited (e.g., 38 mA) to avoid exceeding voltage and/or powerthresholds at the terminals 1331-1333. The active communicator 1300 mayinclude a power conditioner 1306, connected in series to the powersupply 1304, configured to prevent the power supply 1304 from filteringout communication signals (e.g., from the AM modem 1310 and/or aconnected field device).

In operation, the active communicator 1300 may operate in tool-powermode and external-power mode. In tool-power mode, a user may connect thefield device 160 to the terminals 1332 and 133, and may connect a shuntto terminals 1331 and 1332 so that current will flow from the terminal1331 to the terminal 1332 and to the connected field device 160. Inexternal-power mode, a user may connect the field device 160 toterminals 1332 and 1333, leaving an open circuit between terminals 1331and 1332.

When in external-power mode, the switches 1332 and 1324 may be activatedto switch out the bus 1302 and create an open circuit between theterminals 1321-1322 and the wire connecting the power condition 1306 tothe terminal 1331. Further, the DC current controller 1312 may beswitched out of the circuit 1309 when the active communicator 1300 is inexternal-power mode.

The active communicator 1300 may operate in communications mode ordiagnostics mode. When in communications mode, the active communicator1300 may communicate with the connected field device 160. When indiagnostics mode, the active communicator 1300 may measure electricalattributes of signals on a communication bus (e.g., a Fieldbus segment),and/or may measure electrical attributes of signals received at theterminals of the field device 160. When in diagnostics mode, DC currentcontroller 1312 may not draw a significant current. When incommunications mode, the DC current controller 1312 may draw a current(e.g., 11 mA). In some cases, the active communicator 1300 may operatein communications mode and diagnostics mode simultaneously.

If desired, the control unit 402 may disable one or more of the powersupply 1304, the power condition 1306, the terminators 1321/1322, and/orthe circuit 1309 when a change in voltage or current is detected at theterminals 1331-1333. For example, a detected high voltage across theterminals 1332 and 1333 may indicate that a user has attached a newpower source, which may cause the active communicator 1300 to disableone or more components. As another example, a detected high current atthe terminals 1332 and 1333 may indicate that a user has shorted wiresor attempted to add another device, and may cause the activecommunicator 1300 to disable one or more components. For example, a lowvoltage measurement may indicate that an externally powered field devicehas lost power. A low current measurement may indicate a device has beenremoved from the terminals 1331-1333.

The control unit 402 may include a circuit manager routine 1361 formanaging the active communicator 1300 and/or a diagnostics managerroutine 1362 for analyzing signals sent and/or received by the activecommunicator 1300. The circuit manager 1361 may switch out the circuit1309 to protect a current limited connection from having its currentlimit exceeded due to the current load of the circuit 1309. Further, auser may interact with the UI 410 to turn off the power supply 1304 atany time.

Further, the circuit manager 1361 may compensate for signal measurementerror caused by the fuse 1342. That is, the circuit manager 1361 mayaccount for the resistance of the fuse 1342 (which may be roughly 11ohms in some cases) as well as the resistance of the terminators 1321and 1322 when calculating current measurements based on voltage drops onthe bus 1302 associated with communication signals.

The diagnostics manager 1362 may: (i) identify field devices, (ii)detect and analyze electrical characteristics of signals sent and/orreceived by the active communicator 1300, (iii) log measurements and/oranalysis performed over time, and/or (iv) perform a noise spectrumanalysis.

First, the diagnostics manager 1362 may identify field devices connectedto the bus 1302 (or connected to an external bus to which the activecommunicator 1300 is connected) by tag or device ID. The diagnosticsmanager 1362 may enable a user to create a user selectable device listthat the user can select during creation of a log file to define filename, bus name, and/or location name (e.g., a user customizable stringsuch as “storage tank 157”).

Second, the diagnostics manager 1362 may detect and analyze electricalcharacteristics of signals sent and/or received by the activecommunicator 1300. These measurements may be displayed to a user via thedisplay 122 shown in FIGS. 1 and 4. Further, the circuit manager 1361may rely on these measurements to activate or deactivate components ofthe tool 100 (e.g., to protect the components and/or to ensurecompliance with IS standards).

Third, the diagnostics manager 1362 may log the measurements and/or theanalysis performed over time. For example, the diagnostics manager maycreate a health report representing “snapshots” taken over time. As anexample, a user may utilize the tool 100 to measure signals associatedwith a given field device on a fairly regular basis (e.g., every day,once a week, etc.) The diagnostics manager 1362 may log thesemeasurements, enabling plant personnel to identify trends over timeassociated with the field device. The health report may identify a busby a tag or ID of the lowest address device on the bus. The healthreport may include information identifying the user of the tool 100 atthe time relevant measurements were taken, the date of the relevantmeasurements, the bus or segment name where the measurements were taken,and/or the name of the location where the measurements were taken. Thetool 100 may retrieve some of this information from the field device(e.g., the tag or segment name).

As another example of time-based signal analysis and logging, thediagnostics manager 1362 may create a troubleshooting log forcontinuously monitoring a field device's signals over a given timeperiod. For example, a plant may be experiencing issues with aparticular field device (e.g., communication disruptions), but may beunable to determine the cause of the issues. A user may connect the tool100 to the field device and leave the tool 100 for an extended period oftime (e.g., for a number of hours or days). The tool 100 may thenmeasure and log electrical characteristics of transmitter and/orreceived signals on a regular interval and/or based on a trigger (e.g.,signals dropping above or below a threshold). A user can later analyzethe log to identify when the field device is suffering problems, and todetermine what might correlate with the field device suffering problems.For example, by comparing the log to historian data collected by theprocess control system, the user may determine that disruptionsexperienced by the field device are associated with a start-up of anearby motor, which is causing vibrations that disrupt the fielddevice's communications. The troubleshooting log may include the sametype of information as that included in the health report (e.g., a tag,time, date, etc.).

Fourth, the diagnostics manager 1362 may perform a noise spectrumanalysis. In particular, the diagnostics manager 1362 may detectvoltages at a small frequency range (e.g., less than 1 kHz) associatedwith noise and may display the detected voltages so that a user canidentify one or more of: (i) a frequency of the noise; (ii) an amplitudeof the noise (e.g., average or maximum); and/or (iii) a time at which anoise burst occurs.

FIG. 14A is a schematic of the active communicator 1300 connected to afield device 1405 via an external bus 1420 (i.e., external to the activecommunicator 1300), demonstrating an example in which the activecommunicator 1300 is connected to a field device connected to anoperational bus.

An external power supply 1410 (e.g., a rack-mounted power supply) maysupply power to the external bus 1420, and the field device 1405 maydraw power from the external bus 1420. The field device 1405 may draw acurrent of 10-25 mA for power. For example, the field device 1405 maydraw a current of 20 mA, which may be supplied by the power supply 1410.In some cases, multiple field devices may be connected to the bus 1420and may draw power. For example, three field devices may draw 20 mA eachfrom the bus 1420. In such an example, the power supply 1410 may supply60 mA of current to the bus 1420 for power. A power conditioner (notshown) may be placed between the power supply 1410 and the bus 1420.

The field device 1405 may be connected to the Fieldbus segment 1420 viaa Fieldbus spur. The spur may be a two-wire link that connects to thesegment 1420 via a junction box, which may connect multiple other spursto the segment 1420. Due to the multiple links and connection pointsassociated with the Fieldbus segment 1420, it can be difficult toisolate a point of failure. Advantageously, the communicator 1300 cannot only communicate with the field device 1405, but can connect to thesegment 1420 in place of the field device to “see” what the field device1405 is “seeing.” In short, the tool 100 is a “known good device.” If acommunication problem exists between a field device and a controller,the tool 100 can connect to and test the field device. If the fielddevice functions properly when connected to the tool 100, a user of thetool 100 knows the problem exists “upstream” of the field device (e.g.,at a spur, junction box, I/O cards, or some other cable or device).Accordingly, the user can keep moving upstream and testingcommunications to isolate the “bad” device or communication link.

The power supply 1410 may supply power to the field device 1405 via thesegment 1420, as well as to potentially other field devices connected tothe segment 1420.

The segment 1420 may carry a 10-25 mA DC power signal for powering thefield device 1405 and an AC digital communication signal utilized by thefield device 1405. Generally speaking, multiple other field devices mayconnect to the segment 1420, each drawing a 10-25 mA DC signal forpower. Accordingly, the DC current supplied to the segment 1405 by thepower supply 1410 may vary depending on the number of field devices thatconnect to the segment 1420 and draw power. The segment 1420 may includeterminators 1422 and 1424. Each of the terminators 1422 and 1424 mayinclude, e.g., a 100 ohm resistor in series with a 1 μF capacitor.Accordingly, the terminators 1422 and 1422 may block DC current and actas a current shunt for the AC communication signal.

In operation, the active communicator 1300 and field device 1405 maycommunicate by way of a digital signal (e.g., 20 mA peak-to-peak)superimposed on the power signal on the bus 1420. Generally, only onedevice connected to the bus 1420 may communicate at any given time. Forexample, if the active communicator 1300, field device 1405, and twoother field devices (not shown) share the bus 1420, only one of the fourconnected devices may communicate at a given time. Communication on thebus 1420 may be coordinated by a device designated as a Link ActiveScheduler (LAS). The LAS may be responsible for passing a token betweendevices connected to the bus 1420, where only the device with the tokenmay communicate over the bus 1420. In some cases, the field device 1405may be the LAS; in other cases, the tool 100 may be the LAS.

The LAS maintains a list of all devices needing to access the bus 1420.This list may be called a “Live Device List.” In some circumstances, thebus 1420 may have only a single LAS. Devices capable of becoming a LASmay be called link master devices. All other devices may be referred toas “basic devices.” If desired, the tool 100 may be a link masterdevice. When the active communicator 1300 is connected to the bus 1420,the tool 100 may bid to become the LAS. The link master that wins thebid (e.g., the one with the lowest address) may begin operating as theLAS immediately upon completion of the bidding process.

FIG. 14B is a schematic of the active communicator 1300 connected to afield device 1455 via the bus 1302, demonstrating an example in whichthe active communicator 1300 provides power to the field device 1455. Auser may place a shunt 1460 between terminals 1331 and 1332, enablingthe power supply 1304 to supply power to the bus 1302. The power supply1302 may be current limited so that current flowing via the shunt 1460remains under a maximum threshold consistent with IS standards. Forexample, the threshold may be between 35-45 mA. As noted, the DC currentcontroller 1312 may draw 11 mA. Further, typical field devices may draw10-25 mA. The power supply 1302 may be configured to supply up to 36 mAto ensure that the DC current controller 1312 and the field device 1455receive sufficient current (i.e., based on an expected potential totalcurrent draw of 11 mA+25 mA) while remaining IS compliant. The powersupply 1304 may be configured to supply a maximum current of 38 mA. Auser may utilize the active communicator 1300 to supply power to thefield device 1455, to communicate with the field device 1455, and/or toperform diagnostics on the field device 1455 while complying with ISstandards.

FIG. 15 is a view of the communication interface 406 of the tool 100from a perspective external to the tool 100. As shown, the tool 100includes the active communicator 600 and the active communicator 1300,shown in FIGS. 6 and 13, respectively. In some cases, the tool 100includes only one of the active communicator 600 and the activecommunicator 1300.

The communication interface 406 may include the terminals 1331-1333shown in FIG. 13 and the terminals 631-636 shown in FIG. 6, which may bearranged as terminal sets 1501-1504.

In operation, a user may connect the terminal set 1501 to a field deviceconfigured to communicate according to an AM communication scheme, suchas the Fieldbus protocol. The user may utilize the terminal set 1501when connecting the tool 100 to a field device relying on an externalpower supply (i.e., external relative to the tool 100), such as arack-mounted power supply typically found in plant environments. If theuser wishes to utilize the tool 100 to power the field device, the usermay connect terminals 1331 and 1332 using a shunt.

As another example, a user may connect the terminal set 1502 to a fielddevice that requires power and that is configured to communicateaccording to a DC current signaling scheme (e.g., 4-20 mA) and/oraccording to a digital FM communication scheme (e.g., the HART protocol)and that requires power. Alternatively, if the user wants to connect thetool 100 to a similarly configured field device that is already poweredby an external power supply, the user may connect the field device tothe terminal set 1503. A user may also connect the terminal set 1502 toa field device, or to a communication link connected to the fielddevice, to detect the electrical characteristics (e.g., current,voltage) of signals transmitted by the field device or received by thefield device.

Finally, a user may connect the terminal set 1504 to a field device todetect the electrical characteristics (e.g., current, voltage) ofsignals transmitted by the field device or received by the field device.The user may also connect the terminal set 1504 to a communication link(e.g., a HART loop or Fieldbus segment) to detect the electricalcharacteristics of signals transmitted via the communication link. Insome cases, the power monitor 408 connected to the terminal set 1504does nothing but measure current.

As shown, the communication interface 406 enables the tool 100 tocommunicate with or diagnose field devices configured according todifferent protocols. Thus, a user may carry the tool 100 to servicemultiple different types of field devices rather than carrying multiplespecialized tools.

What is claimed is:
 1. A portable field maintenance tool comprising: (A)a housing; (B) a communication interface that is disposed through thehousing, the communication interface including an internal portionaccessible within the housing and a set of terminals accessible outsidethe housing, the set of terminals electrically connectable to a fielddevice by way of a wired link configured to carry a composite signalincluding: (i) a communication signal transmitted to or from the fielddevice, and (ii) a power signal transmitted to the field device; (C) acommunication circuit disposed within the housing and electricallyconnected to the internal portion of the communication interface, thecommunication circuit configured to encode or decode the communicationsignal; and (D) a power supply disposed within the housing andelectrically connected to the internal portion of the communicationinterface and to the communication circuit, the power supply configuredto transmit the power signal; wherein the communication circuit includesa resistor network having a resistance within a range to cause a voltagedrop, at the set of terminals, associated with the composite signal, thevoltage drop being: (i) above a minimum voltage threshold associatedwith reading the composite signal, and (ii) below a maximum voltagethreshold.
 2. The portable field maintenance tool of claim 1, whereinthe communication circuit and the power supply are each configured forintrinsically safe operation.
 3. The portable field maintenance tool ofclaim 1, wherein the communication circuit includes a DC currentcontroller and a digital frequency modulation (FM) modem, and whereinthe composite signal includes: (i) an analog DC signal that includes thepower signal and that varies in amplitude to convey information; and(ii) a digital FM communication signal superimposed on the analog DCsignal.
 4. The portable field maintenance tool of claim 1, wherein theminimum voltage threshold is a minimum peak-to-peak voltage associatedwith reading the communication signal.
 5. The portable field maintenancetool of claim 1, wherein the maximum voltage threshold is below avoltage sufficient to generate a spark at the set of terminals.
 6. Theportable field maintenance tool of claim 1, wherein the power supply isconfigured to transmit the power signal at a voltage that is at or belowthe maximum voltage threshold.
 7. The portable field maintenance tool ofclaim 6, wherein the maximum voltage threshold is a value between 10 Vand 30 V.
 8. The portable field maintenance tool of claim 7, wherein themaximum voltage threshold is a value between 21 V and 24 V.
 9. Theportable field maintenance tool of claim 1, wherein the minimum voltagethreshold is a value between 50 mV peak-to-peak and 500 mV peak-to-peak.10. The portable field maintenance tool of claim 1, wherein the minimumvoltage threshold is a value of 120 mV peak-to-peak.
 11. The portablefield maintenance tool of claim 1, wherein the resistor network includesone or more resistors exceeding 2 mm in length and exceeding 2 mm inwidth so that the one or more resistors have sufficient surface area toprotect against a temperature spike above a temperature threshold. 12.The portable field maintenance tool of claim 1, wherein the range is 75Ohms to 750 ohms.
 13. The portable field maintenance tool of claim 1,wherein the resistor network includes a plurality of resistors.
 14. Theportable field maintenance tool of claim 13, wherein the plurality ofresistors are arranged such that the resistor network maintains theresistance within the range when any one of the plurality of resistorsfails.
 15. The portable field maintenance tool of claim 13, wherein theresistor network includes a plurality of switches, each of the pluralityof switches in series with a one of the plurality of resistors andactuatable to: (i) remove the one of the plurality of resistors from theresistor network, or (ii) add the one of the plurality of resistors tothe resistor network.
 16. The portable field maintenance tool of claim15, wherein each of the plurality of switches is a solid state relay.17. The portable field maintenance tool of claim 15, wherein aresistance of each of the plurality of resistors is selected so thateach of the plurality of switches is actuatable to adjust the resistanceof the resistor network to a value within a range of 75 ohms and 750ohms.
 18. The portable field maintenance tool of claim 1, wherein theresistor network includes a first resistor sub-network arranged inparallel with a second resistor sub-network.
 19. The portable fieldmaintenance tool of claim 18, wherein the resistor network furtherincludes a third resistor sub-network arranged in parallel with thefirst resistor sub-network and the second resistor sub-network.
 20. Theportable field maintenance tool of claim 19, wherein: the first resistorsub-network has a resistance between 200 ohms and 300 ohms; the secondresistor sub-network has a resistance between 400 ohms and 600 ohms; andthe third resistor sub-network has a resistance between 700 ohms and 800ohms.
 21. The portable field maintenance tool of claim 1, furthercomprising a fuse electrically connected to the communication interface,the fuse configured to limit a current at the communication interface tobelow a current threshold.
 22. The portable field maintenance tool ofclaim 21, wherein the current threshold is a value between 10 mA and 150mA.
 23. The portable field maintenance tool of claim 21, wherein thecurrent threshold is 50 mA.
 24. The portable field maintenance tool ofclaim 1, wherein the set of terminals includes: (i) a positive terminalconnectable to a first wire of the wired link, and (ii) a negativeterminal connectable to a second wire of the wired link.
 25. Theportable field maintenance tool of claim 1, wherein the wired link isconnected to the field device via a second wired link connected to thefield device.
 26. A method of communicating with a transmitter fielddevice, the method comprising: communicatively connecting, via a wiredlink, a set of terminals of a portable field maintenance tool to atransmitter field device; supplying power from the portable fieldmaintenance tool, via the wired link, to the transmitter field device;receiving by the portable field maintenance tool, via the wired link, acommunication signal superimposed on the supplied power; and limiting avoltage drop at the set of terminals, associated with the communicationsignal and the supplied power, to between a minimum voltage thresholdand a maximum voltage threshold by: (i) limiting the supplied power sothat the voltage drop does not exceed the maximum voltage threshold; and(ii) activating or deactivating one or more resistors of a resistornetwork disposed within the portable field maintenance tool andelectrically connected to the set of terminals so that the voltage dropremains above the minimum voltage threshold.
 27. The method of claim 26,wherein the communication signal is an analog DC signal that varies inamplitude to convey information and that is superimposed on the suppliedpower.
 28. The method of claim 26, wherein activating or deactivatingthe one or more resistors of the resistor network disposed within theportable field maintenance tool so that the voltage drop remains abovethe minimum voltage threshold comprises: activating or deactivating theone or more resistors of the resistor network so that the voltage dropexceeds a minimum peak-to-peak voltage associated with reading thecommunication signal.
 29. The method of claim 28, wherein the minimumpeak-to-peak voltage is a value between 100 mV peak-to-peak and 250 mVpeak-to-peak.
 30. The method of claim 28, wherein activating ordeactivating the one or more resistors of the resistor networkcomprises: activating or deactivating one or more switches, eacharranged in series with a one of the one or more resistors.
 31. A methodof communicating with an actuator field device comprising:communicatively connecting, via a wired link, a set of terminals of aportable field maintenance tool to an actuator field device; supplyingpower from the portable field maintenance tool, via the wired link, tothe actuator field device; limiting the supplied power so that the setof terminals do not exceed a maximum electrical threshold; andtransmitting by the portable field maintenance tool, via the wired link,to the actuator field device a communication signal superimposed on thesupplied power.
 32. The method of claim 31, wherein limiting thesupplied power so that the set of terminals do not exceed a maximumelectrical threshold comprises: limiting the supplied power so that avoltage drop at the set of terminals does not exceed a maximum voltagethreshold, wherein the maximum voltage threshold is any value between 21V and 24 V.
 33. The method of claim 31, wherein limiting the suppliedpower so that the set of terminals do not exceed a maximum electricalthreshold comprises: limiting the supplied power so that power availableat the set of terminals does not exceed a maximum power threshold,wherein the maximum power threshold is any value between 0.25 W and 1.5W.
 34. The method of claim 31, wherein limiting the supplied power sothat the set of terminals do not exceed a maximum electrical thresholdcomprises: inducing a first voltage drop across an internal resistor tokeep a second voltage drop at the set of terminals below a maximumvoltage threshold.
 35. The method of claim 31, wherein limiting thesupplied power so that the set of terminals do not exceed a maximumelectrical threshold comprises: disabling the portable field maintenancetool when a voltage at the set of terminals exceeds a maximum voltagethreshold; or disabling the portable field maintenance tool when acurrent at the set of terminals exceeds a maximum current threshold. 36.A portable field maintenance tool comprising: a set of terminalselectrically connectable, via a wired link, to a field device thattransmits or receives a signal via the wired link; a communicationcircuit, electrically connected to the set of terminals, that receivesor transmits the signal via the set of terminals; and an energymeasurement circuit, electrically connected to the set of terminals,that measures one or more electrical characteristics of the signal atthe set of terminals.
 37. The portable field maintenance tool of claim36, further comprising: a resistor network; and a control unit,communicatively coupled to the energy measurement circuit, thatactivates or deactivates one or more resistors of the resistor networkbased on the measured one or more electrical characteristics.
 38. Theportable field maintenance tool of claim 36, further comprising a powersupply that supplies power via the wired link.
 39. The portable fieldmaintenance tool of claim 38, further comprising a control unit,communicatively coupled to the energy measurement circuit and to thepower supply, that controls the power supply based on the measured oneor more electrical characteristics.
 40. The portable field maintenancetool of claim 39, wherein the control unit controls the power supply toprevent the set of terminals from exceeding a maximum power threshold byreducing a supplied voltage in order to prevent the set of terminalsfrom exceeding the maximum power threshold.
 41. The portable fieldmaintenance tool of claim 36, wherein the signal is a composite signalincluding a communication signal and a power signal.
 42. The portablefield maintenance tool of claim 38, wherein the communication signal isa digital FM communication signal; and wherein the communication circuitincludes an FM modem that transmits or receives the digital FMcommunication signals.
 43. A method of communicating with a field deviceand monitoring signals sent or received by the field device, the methodcomprising: electrically connecting, via a wired link, a field device toa set of terminals of a portable field maintenance tool; transmitting orreceiving, at the set of terminals of the portable field maintenancetool, a signal to or from the field device; and measuring, at the set ofterminals, one or more electrical characteristics of the transmitted orreceived signal.
 44. The method of claim 43, wherein the measuringoccurs simultaneously with the transmitting or receiving.
 45. The methodof claim 43, further comprising: maintaining a voltage drop at the setof terminals to a value above a minimum voltage threshold necessary toread the signal by activating or deactivating one or more resistors ofthe portable field maintenance tool based on the measured one or moreelectrical characteristics.
 46. The method of claim 43, furthercomprising disabling the portable field maintenance tool when the signalon the wired link exceeds a maximum electrical threshold or drops belowa minimum electrical threshold.
 47. The method of claim 46, wherein themaximum electrical threshold is a maximum power threshold or a maximumcurrent threshold, and wherein the minimum electrical threshold is aminimum voltage threshold or a minimum current threshold.
 48. The methodof claim 43, further comprising: supplying power from the portable fieldmaintenance tool, via the wired link, to the field device.
 49. Themethod of claim 48, further comprising: adjusting the supplied power toprevent the set of terminals from exceeding a maximum electricalthreshold, wherein the maximum electrical threshold is a maximum powerthreshold between 0.25 W and 1.5 W.
 50. The method of claim 48, furthercomprising: stopping the supplying of power; and raising a loopresistance to bleed off voltage associated with the supplying of powerby activating or deactivating one or more resistors of the portablefield maintenance tool.
 51. The method of claim 43, further comprising:performing an analysis of the one or more electrical characteristics todetermine whether or not the field device is connected to an externalloop resistor; preventing an internal loop resistor from activating whenthe analysis reveals that the field device is connected to an externalloop resistor; and activating the internal loop resistor when theanalysis reveals that the field device is not connected to an externalloop resistor.
 52. The method of claim 43, further comprising: detectingvoltage decay at the set of terminals; and enabling activation of apower supply based on the detected voltage decay.